[reactos] 01/02: [MBEDTLS] Update to version 2.7.13. CORE-16686

[Thomas Faber]

https://git.reactos.org/?p=reactos.git;a=commitdiff;h=d152519a4acf6e36bed83…

commit d152519a4acf6e36bed83f5e30d5bc44fa7db754
Author:     Thomas Faber <thomas.faber(a)reactos.org>
AuthorDate: Sun Feb 9 20:56:36 2020 +0100
Commit:     Thomas Faber <thomas.faber(a)reactos.org>
CommitDate: Sun Feb 9 21:23:22 2020 +0100

    [MBEDTLS] Update to version 2.7.13. CORE-16686
---
 dll/3rdparty/mbedtls/aes.c                      |  24 ++
 dll/3rdparty/mbedtls/bignum.c                   |  97 ++++++++
 dll/3rdparty/mbedtls/ctr_drbg.c                 | 112 ++++-----
 dll/3rdparty/mbedtls/ecdsa.c                    |   1 +
 dll/3rdparty/mbedtls/ecp.c                      |  10 +-
 dll/3rdparty/mbedtls/hmac_drbg.c                |  25 +-
 media/doc/3rd Party Files.txt                   |   2 +-
 sdk/include/reactos/libs/mbedtls/bignum.h       |  20 +-
 sdk/include/reactos/libs/mbedtls/check_config.h |   8 +
 sdk/include/reactos/libs/mbedtls/config.h       |   4 +
 sdk/include/reactos/libs/mbedtls/ctr_drbg.h     | 217 +++++++++++++----
 sdk/include/reactos/libs/mbedtls/hmac_drbg.h    | 296 +++++++++++++++---------
 12 files changed, 588 insertions(+), 228 deletions(-)

diff --git a/dll/3rdparty/mbedtls/aes.c b/dll/3rdparty/mbedtls/aes.c
index fed58bbc010..6004e80ab00 100644
--- a/dll/3rdparty/mbedtls/aes.c
+++ b/dll/3rdparty/mbedtls/aes.c
@@ -763,6 +763,18 @@ int mbedtls_internal_aes_encrypt( mbedtls_aes_context *ctx,
     PUT_UINT32_LE( X2, output,  8 );
     PUT_UINT32_LE( X3, output, 12 );
 
+    mbedtls_zeroize( &X0, sizeof( X0 ) );
+    mbedtls_zeroize( &X1, sizeof( X1 ) );
+    mbedtls_zeroize( &X2, sizeof( X2 ) );
+    mbedtls_zeroize( &X3, sizeof( X3 ) );
+
+    mbedtls_zeroize( &Y0, sizeof( Y0 ) );
+    mbedtls_zeroize( &Y1, sizeof( Y1 ) );
+    mbedtls_zeroize( &Y2, sizeof( Y2 ) );
+    mbedtls_zeroize( &Y3, sizeof( Y3 ) );
+
+    mbedtls_zeroize( &RK, sizeof( RK ) );
+
     return( 0 );
 }
 #endif /* !MBEDTLS_AES_ENCRYPT_ALT */
@@ -831,6 +843,18 @@ int mbedtls_internal_aes_decrypt( mbedtls_aes_context *ctx,
     PUT_UINT32_LE( X2, output,  8 );
     PUT_UINT32_LE( X3, output, 12 );
 
+    mbedtls_zeroize( &X0, sizeof( X0 ) );
+    mbedtls_zeroize( &X1, sizeof( X1 ) );
+    mbedtls_zeroize( &X2, sizeof( X2 ) );
+    mbedtls_zeroize( &X3, sizeof( X3 ) );
+
+    mbedtls_zeroize( &Y0, sizeof( Y0 ) );
+    mbedtls_zeroize( &Y1, sizeof( Y1 ) );
+    mbedtls_zeroize( &Y2, sizeof( Y2 ) );
+    mbedtls_zeroize( &Y3, sizeof( Y3 ) );
+
+    mbedtls_zeroize( &RK, sizeof( RK ) );
+
     return( 0 );
 }
 #endif /* !MBEDTLS_AES_DECRYPT_ALT */
diff --git a/dll/3rdparty/mbedtls/bignum.c b/dll/3rdparty/mbedtls/bignum.c
index 62314c5bcd5..596e1a0164e 100644
--- a/dll/3rdparty/mbedtls/bignum.c
+++ b/dll/3rdparty/mbedtls/bignum.c
@@ -921,6 +921,103 @@ int mbedtls_mpi_cmp_mpi( const mbedtls_mpi *X, const mbedtls_mpi *Y
)
     return( 0 );
 }
 
+/** Decide if an integer is less than the other, without branches.
+ *
+ * \param x         First integer.
+ * \param y         Second integer.
+ *
+ * \return          1 if \p x is less than \p y, 0 otherwise
+ */
+static unsigned ct_lt_mpi_uint( const mbedtls_mpi_uint x,
+        const mbedtls_mpi_uint y )
+{
+    mbedtls_mpi_uint ret;
+    mbedtls_mpi_uint cond;
+
+    /*
+     * Check if the most significant bits (MSB) of the operands are different.
+     */
+    cond = ( x ^ y );
+    /*
+     * If the MSB are the same then the difference x-y will be negative (and
+     * have its MSB set to 1 during conversion to unsigned) if and only if x<y.
+     */
+    ret = ( x - y ) & ~cond;
+    /*
+     * If the MSB are different, then the operand with the MSB of 1 is the
+     * bigger. (That is if y has MSB of 1, then x<y is true and it is false if
+     * the MSB of y is 0.)
+     */
+    ret |= y & cond;
+
+
+    ret = ret >> ( biL - 1 );
+
+    return (unsigned) ret;
+}
+
+/*
+ * Compare signed values in constant time
+ */
+int mbedtls_mpi_lt_mpi_ct( const mbedtls_mpi *X, const mbedtls_mpi *Y,
+        unsigned *ret )
+{
+    size_t i;
+    /* The value of any of these variables is either 0 or 1 at all times. */
+    unsigned cond, done, X_is_negative, Y_is_negative;
+
+    if( X->n != Y->n )
+        return MBEDTLS_ERR_MPI_BAD_INPUT_DATA;
+
+    /*
+     * Set sign_N to 1 if N >= 0, 0 if N < 0.
+     * We know that N->s == 1 if N >= 0 and N->s == -1 if N < 0.
+     */
+    X_is_negative = ( X->s & 2 ) >> 1;
+    Y_is_negative = ( Y->s & 2 ) >> 1;
+
+    /*
+     * If the signs are different, then the positive operand is the bigger.
+     * That is if X is negative (X_is_negative == 1), then X < Y is true and it
+     * is false if X is positive (X_is_negative == 0).
+     */
+    cond = ( X_is_negative ^ Y_is_negative );
+    *ret = cond & X_is_negative;
+
+    /*
+     * This is a constant-time function. We might have the result, but we still
+     * need to go through the loop. Record if we have the result already.
+     */
+    done = cond;
+
+    for( i = X->n; i > 0; i-- )
+    {
+        /*
+         * If Y->p[i - 1] < X->p[i - 1] then X < Y is true if and only if
both
+         * X and Y are negative.
+         *
+         * Again even if we can make a decision, we just mark the result and
+         * the fact that we are done and continue looping.
+         */
+        cond = ct_lt_mpi_uint( Y->p[i - 1], X->p[i - 1] );
+        *ret |= cond & ( 1 - done ) & X_is_negative;
+        done |= cond;
+
+        /*
+         * If X->p[i - 1] < Y->p[i - 1] then X < Y is true if and only if
both
+         * X and Y are positive.
+         *
+         * Again even if we can make a decision, we just mark the result and
+         * the fact that we are done and continue looping.
+         */
+        cond = ct_lt_mpi_uint( X->p[i - 1], Y->p[i - 1] );
+        *ret |= cond & ( 1 - done ) & ( 1 - X_is_negative );
+        done |= cond;
+    }
+
+    return( 0 );
+}
+
 /*
  * Compare signed values
  */
diff --git a/dll/3rdparty/mbedtls/ctr_drbg.c b/dll/3rdparty/mbedtls/ctr_drbg.c
index f105391cc6e..1173f2209dc 100644
--- a/dll/3rdparty/mbedtls/ctr_drbg.c
+++ b/dll/3rdparty/mbedtls/ctr_drbg.c
@@ -68,56 +68,6 @@ void mbedtls_ctr_drbg_init( mbedtls_ctr_drbg_context *ctx )
 #endif
 }
 
-/*
- * Non-public function wrapped by mbedtls_ctr_drbg_seed(). Necessary to allow
- * NIST tests to succeed (which require known length fixed entropy)
- */
-int mbedtls_ctr_drbg_seed_entropy_len(
-                   mbedtls_ctr_drbg_context *ctx,
-                   int (*f_entropy)(void *, unsigned char *, size_t),
-                   void *p_entropy,
-                   const unsigned char *custom,
-                   size_t len,
-                   size_t entropy_len )
-{
-    int ret;
-    unsigned char key[MBEDTLS_CTR_DRBG_KEYSIZE];
-
-    memset( key, 0, MBEDTLS_CTR_DRBG_KEYSIZE );
-
-    mbedtls_aes_init( &ctx->aes_ctx );
-
-    ctx->f_entropy = f_entropy;
-    ctx->p_entropy = p_entropy;
-
-    ctx->entropy_len = entropy_len;
-    ctx->reseed_interval = MBEDTLS_CTR_DRBG_RESEED_INTERVAL;
-
-    /*
-     * Initialize with an empty key
-     */
-    if( ( ret = mbedtls_aes_setkey_enc( &ctx->aes_ctx, key,
MBEDTLS_CTR_DRBG_KEYBITS ) ) != 0 )
-    {
-        return( ret );
-    }
-
-    if( ( ret = mbedtls_ctr_drbg_reseed( ctx, custom, len ) ) != 0 )
-    {
-        return( ret );
-    }
-    return( 0 );
-}
-
-int mbedtls_ctr_drbg_seed( mbedtls_ctr_drbg_context *ctx,
-                   int (*f_entropy)(void *, unsigned char *, size_t),
-                   void *p_entropy,
-                   const unsigned char *custom,
-                   size_t len )
-{
-    return( mbedtls_ctr_drbg_seed_entropy_len( ctx, f_entropy, p_entropy, custom, len,
-                                       MBEDTLS_CTR_DRBG_ENTROPY_LEN ) );
-}
-
 void mbedtls_ctr_drbg_free( mbedtls_ctr_drbg_context *ctx )
 {
     if( ctx == NULL )
@@ -388,6 +338,52 @@ exit:
     return( ret );
 }
 
+int mbedtls_ctr_drbg_seed( mbedtls_ctr_drbg_context *ctx,
+                           int (*f_entropy)(void *, unsigned char *, size_t),
+                           void *p_entropy,
+                           const unsigned char *custom,
+                           size_t len )
+{
+    int ret;
+    unsigned char key[MBEDTLS_CTR_DRBG_KEYSIZE];
+
+    memset( key, 0, MBEDTLS_CTR_DRBG_KEYSIZE );
+
+    mbedtls_aes_init( &ctx->aes_ctx );
+
+    ctx->f_entropy = f_entropy;
+    ctx->p_entropy = p_entropy;
+
+    if( ctx->entropy_len == 0 )
+        ctx->entropy_len = MBEDTLS_CTR_DRBG_ENTROPY_LEN;
+    ctx->reseed_interval = MBEDTLS_CTR_DRBG_RESEED_INTERVAL;
+
+    /*
+     * Initialize with an empty key
+     */
+    if( ( ret = mbedtls_aes_setkey_enc( &ctx->aes_ctx, key,
MBEDTLS_CTR_DRBG_KEYBITS ) ) != 0 )
+    {
+        return( ret );
+    }
+
+    if( ( ret = mbedtls_ctr_drbg_reseed( ctx, custom, len ) ) != 0 )
+    {
+        return( ret );
+    }
+    return( 0 );
+}
+
+/* Backward compatibility wrapper */
+int mbedtls_ctr_drbg_seed_entropy_len(
+    mbedtls_ctr_drbg_context *ctx,
+    int (*f_entropy)(void *, unsigned char *, size_t), void *p_entropy,
+    const unsigned char *custom, size_t len,
+    size_t entropy_len )
+{
+    mbedtls_ctr_drbg_set_entropy_len( ctx, entropy_len );
+    return( mbedtls_ctr_drbg_seed( ctx, f_entropy, p_entropy, custom, len ) );
+}
+
 int mbedtls_ctr_drbg_random_with_add( void *p_rng,
                               unsigned char *output, size_t output_len,
                               const unsigned char *additional, size_t add_len )
@@ -459,7 +455,7 @@ int mbedtls_ctr_drbg_random_with_add( void *p_rng,
 exit:
     mbedtls_zeroize( add_input, sizeof( add_input ) );
     mbedtls_zeroize( tmp, sizeof( tmp ) );
-    return( 0 );
+    return( ret );
 }
 
 int mbedtls_ctr_drbg_random( void *p_rng, unsigned char *output, size_t output_len )
@@ -619,8 +615,11 @@ int mbedtls_ctr_drbg_self_test( int verbose )
         mbedtls_printf( "  CTR_DRBG (PR = TRUE) : " );
 
     test_offset = 0;
-    CHK( mbedtls_ctr_drbg_seed_entropy_len( &ctx, ctr_drbg_self_test_entropy,
-                                (void *) entropy_source_pr, nonce_pers_pr, 16, 32 ) );
+    mbedtls_ctr_drbg_set_entropy_len( &ctx, 32 );
+    CHK( mbedtls_ctr_drbg_seed( &ctx,
+                                ctr_drbg_self_test_entropy,
+                                (void *) entropy_source_pr,
+                                nonce_pers_pr, 16 ) );
     mbedtls_ctr_drbg_set_prediction_resistance( &ctx, MBEDTLS_CTR_DRBG_PR_ON );
     CHK( mbedtls_ctr_drbg_random( &ctx, buf, MBEDTLS_CTR_DRBG_BLOCKSIZE ) );
     CHK( mbedtls_ctr_drbg_random( &ctx, buf, MBEDTLS_CTR_DRBG_BLOCKSIZE ) );
@@ -640,8 +639,11 @@ int mbedtls_ctr_drbg_self_test( int verbose )
     mbedtls_ctr_drbg_init( &ctx );
 
     test_offset = 0;
-    CHK( mbedtls_ctr_drbg_seed_entropy_len( &ctx, ctr_drbg_self_test_entropy,
-                            (void *) entropy_source_nopr, nonce_pers_nopr, 16, 32 ) );
+    mbedtls_ctr_drbg_set_entropy_len( &ctx, 32 );
+    CHK( mbedtls_ctr_drbg_seed( &ctx,
+                                ctr_drbg_self_test_entropy,
+                                (void *) entropy_source_nopr,
+                                nonce_pers_nopr, 16 ) );
     CHK( mbedtls_ctr_drbg_random( &ctx, buf, 16 ) );
     CHK( mbedtls_ctr_drbg_reseed( &ctx, NULL, 0 ) );
     CHK( mbedtls_ctr_drbg_random( &ctx, buf, 16 ) );
diff --git a/dll/3rdparty/mbedtls/ecdsa.c b/dll/3rdparty/mbedtls/ecdsa.c
index 4f1ce8ad205..9defe41c5c7 100644
--- a/dll/3rdparty/mbedtls/ecdsa.c
+++ b/dll/3rdparty/mbedtls/ecdsa.c
@@ -155,6 +155,7 @@ static int ecdsa_sign_internal( mbedtls_ecp_group *grp, mbedtls_mpi
*r,
         MBEDTLS_MPI_CHK( mbedtls_mpi_add_mpi( &e, &e, s ) );
         MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &e, &e, &t ) );
         MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( &k, &k, &t ) );
+        MBEDTLS_MPI_CHK( mbedtls_mpi_mod_mpi( &k, &k, &grp->N ) );
         MBEDTLS_MPI_CHK( mbedtls_mpi_inv_mod( s, &k, &grp->N ) );
         MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi( s, s, &e ) );
         MBEDTLS_MPI_CHK( mbedtls_mpi_mod_mpi( s, s, &grp->N ) );
diff --git a/dll/3rdparty/mbedtls/ecp.c b/dll/3rdparty/mbedtls/ecp.c
index 5d20db854dd..89d1606a74f 100644
--- a/dll/3rdparty/mbedtls/ecp.c
+++ b/dll/3rdparty/mbedtls/ecp.c
@@ -1959,6 +1959,7 @@ int mbedtls_ecp_gen_privkey( const mbedtls_ecp_group *grp,
     {
         /* SEC1 3.2.1: Generate d such that 1 <= n < N */
         int count = 0;
+        unsigned cmp = 0;
 
         /*
          * Match the procedure given in RFC 6979 (deterministic ECDSA):
@@ -1983,9 +1984,14 @@ int mbedtls_ecp_gen_privkey( const mbedtls_ecp_group *grp,
              */
             if( ++count > 30 )
                 return( MBEDTLS_ERR_ECP_RANDOM_FAILED );
+
+            ret = mbedtls_mpi_lt_mpi_ct( d, &grp->N, &cmp );
+            if( ret != 0 )
+            {
+                goto cleanup;
+            }
         }
-        while( mbedtls_mpi_cmp_int( d, 1 ) < 0 ||
-               mbedtls_mpi_cmp_mpi( d, &grp->N ) >= 0 );
+        while( mbedtls_mpi_cmp_int( d, 1 ) < 0 || cmp != 1 );
     }
 #endif /* ECP_SHORTWEIERSTRASS */
 
diff --git a/dll/3rdparty/mbedtls/hmac_drbg.c b/dll/3rdparty/mbedtls/hmac_drbg.c
index 9a4a1a880e9..27c4a00c46a 100644
--- a/dll/3rdparty/mbedtls/hmac_drbg.c
+++ b/dll/3rdparty/mbedtls/hmac_drbg.c
@@ -277,16 +277,19 @@ int mbedtls_hmac_drbg_seed( mbedtls_hmac_drbg_context *ctx,
 
     ctx->reseed_interval = MBEDTLS_HMAC_DRBG_RESEED_INTERVAL;
 
-    /*
-     * See SP800-57 5.6.1 (p. 65-66) for the security strength provided by
-     * each hash function, then according to SP800-90A rev1 10.1 table 2,
-     * min_entropy_len (in bits) is security_strength.
-     *
-     * (This also matches the sizes used in the NIST test vectors.)
-     */
-    ctx->entropy_len = md_size <= 20 ? 16 : /* 160-bits hash -> 128 bits */
-                       md_size <= 28 ? 24 : /* 224-bits hash -> 192 bits */
-                       32;  /* better (256+) -> 256 bits */
+    if( ctx->entropy_len == 0 )
+    {
+        /*
+         * See SP800-57 5.6.1 (p. 65-66) for the security strength provided by
+         * each hash function, then according to SP800-90A rev1 10.1 table 2,
+         * min_entropy_len (in bits) is security_strength.
+         *
+         * (This also matches the sizes used in the NIST test vectors.)
+         */
+        ctx->entropy_len = md_size <= 20 ? 16 : /* 160-bits hash -> 128 bits */
+                           md_size <= 28 ? 24 : /* 224-bits hash -> 192 bits */
+                           32;  /* better (256+) -> 256 bits */
+    }
 
     if( ( ret = hmac_drbg_reseed_core( ctx, custom, len,
                                        1 /* add nonce */ ) ) != 0 )
@@ -307,7 +310,7 @@ void mbedtls_hmac_drbg_set_prediction_resistance(
mbedtls_hmac_drbg_context *ctx
 }
 
 /*
- * Set entropy length grabbed for reseeds
+ * Set entropy length grabbed for seeding
  */
 void mbedtls_hmac_drbg_set_entropy_len( mbedtls_hmac_drbg_context *ctx, size_t len )
 {
diff --git a/media/doc/3rd Party Files.txt b/media/doc/3rd Party Files.txt
index f0964adf64e..26c1ac441d4 100644
--- a/media/doc/3rd Party Files.txt	
+++ b/media/doc/3rd Party Files.txt	
@@ -83,7 +83,7 @@ Used Version: 4.1.0
 Website: http://www.simplesystems.org/libtiff/
 
 Title: mbed TLS
-Used Version: 2.7.12
+Used Version: 2.7.13
 Website: https://tls.mbed.org/
 
 Title: libpng
diff --git a/sdk/include/reactos/libs/mbedtls/bignum.h
b/sdk/include/reactos/libs/mbedtls/bignum.h
index fd57d90fb28..c0ec3390d60 100644
--- a/sdk/include/reactos/libs/mbedtls/bignum.h
+++ b/sdk/include/reactos/libs/mbedtls/bignum.h
@@ -181,7 +181,7 @@ extern "C" {
  */
 typedef struct
 {
-    int s;              /*!<  integer sign      */
+    int s;              /*!<  Sign: -1 if the mpi is negative, 1 otherwise */
     size_t n;           /*!<  total # of limbs  */
     mbedtls_mpi_uint *p;          /*!<  pointer to limbs  */
 }
@@ -486,6 +486,24 @@ int mbedtls_mpi_cmp_abs( const mbedtls_mpi *X, const mbedtls_mpi *Y
);
  */
 int mbedtls_mpi_cmp_mpi( const mbedtls_mpi *X, const mbedtls_mpi *Y );
 
+/**
+ * \brief          Check if an MPI is less than the other in constant time.
+ *
+ * \param X        The left-hand MPI. This must point to an initialized MPI
+ *                 with the same allocated length as Y.
+ * \param Y        The right-hand MPI. This must point to an initialized MPI
+ *                 with the same allocated length as X.
+ * \param ret      The result of the comparison:
+ *                 \c 1 if \p X is less than \p Y.
+ *                 \c 0 if \p X is greater than or equal to \p Y.
+ *
+ * \return         0 on success.
+ * \return         MBEDTLS_ERR_MPI_BAD_INPUT_DATA if the allocated length of
+ *                 the two input MPIs is not the same.
+ */
+int mbedtls_mpi_lt_mpi_ct( const mbedtls_mpi *X, const mbedtls_mpi *Y,
+        unsigned *ret );
+
 /**
  * \brief          Compare signed values
  *
diff --git a/sdk/include/reactos/libs/mbedtls/check_config.h
b/sdk/include/reactos/libs/mbedtls/check_config.h
index 36927a90cb2..97af2d2d8f3 100644
--- a/sdk/include/reactos/libs/mbedtls/check_config.h
+++ b/sdk/include/reactos/libs/mbedtls/check_config.h
@@ -262,6 +262,14 @@
 #error "MBEDTLS_MEMORY_BUFFER_ALLOC_C defined, but not all prerequisites"
 #endif
 
+#if defined(MBEDTLS_MEMORY_BACKTRACE) && !defined(MBEDTLS_MEMORY_BUFFER_ALLOC_C)
+#error "MBEDTLS_MEMORY_BACKTRACE defined, but not all prerequesites"
+#endif
+
+#if defined(MBEDTLS_MEMORY_DEBUG) && !defined(MBEDTLS_MEMORY_BUFFER_ALLOC_C)
+#error "MBEDTLS_MEMORY_DEBUG defined, but not all prerequesites"
+#endif
+
 #if defined(MBEDTLS_PADLOCK_C) && !defined(MBEDTLS_HAVE_ASM)
 #error "MBEDTLS_PADLOCK_C defined, but not all prerequisites"
 #endif
diff --git a/sdk/include/reactos/libs/mbedtls/config.h
b/sdk/include/reactos/libs/mbedtls/config.h
index 050ca896dea..d339b7c1b14 100644
--- a/sdk/include/reactos/libs/mbedtls/config.h
+++ b/sdk/include/reactos/libs/mbedtls/config.h
@@ -1886,6 +1886,10 @@
  *
  * Enable the CTR_DRBG AES-256-based random generator.
  *
+ * \note This module only achieves a 256-bit security strength if
+ *       the generator is seeded with sufficient entropy.
+ *       See ctr_drbg.h for more details.
+ *
  * Module:  library/ctr_drbg.c
  * Caller:
  *
diff --git a/sdk/include/reactos/libs/mbedtls/ctr_drbg.h
b/sdk/include/reactos/libs/mbedtls/ctr_drbg.h
index eec3f7c8889..0be428b8561 100644
--- a/sdk/include/reactos/libs/mbedtls/ctr_drbg.h
+++ b/sdk/include/reactos/libs/mbedtls/ctr_drbg.h
@@ -1,13 +1,38 @@
 /**
  * \file ctr_drbg.h
  *
- * \brief    CTR_DRBG is based on AES-256, as defined in <em>NIST SP 800-90A:
- *           Recommendation for Random Number Generation Using Deterministic
- *           Random Bit Generators</em>.
- *
+ * \brief    The CTR_DRBG pseudorandom generator.
+ *
+ * CTR_DRBG is a standardized way of building a PRNG from a block-cipher
+ * in counter mode operation, as defined in <em>NIST SP 800-90A:
+ * Recommendation for Random Number Generation Using Deterministic Random
+ * Bit Generators</em>.
+ *
+ * The Mbed TLS implementation of CTR_DRBG uses AES-256
+ * as the underlying block cipher, with a derivation function.
+ * The initial seeding grabs #MBEDTLS_CTR_DRBG_ENTROPY_LEN bytes of entropy.
+ * See the documentation of mbedtls_ctr_drbg_seed() for more details.
+ *
+ * Based on NIST SP 800-90A §10.2.1 table 3 and NIST SP 800-57 part 1 table 2,
+ * here are the security strengths achieved in typical configuration:
+ * - 256 bits under the default configuration of the library,
+ *   with #MBEDTLS_CTR_DRBG_ENTROPY_LEN set to 48 or more.
+ * - 256 bits if #MBEDTLS_CTR_DRBG_ENTROPY_LEN is set
+ *   to 32 or more and the DRBG is initialized with an explicit
+ *   nonce in the \c custom parameter to mbedtls_ctr_drbg_seed().
+ * - 128 bits if #MBEDTLS_CTR_DRBG_ENTROPY_LEN is
+ *   between 24 and 47 and the DRBG is not initialized with an explicit
+ *   nonce (see mbedtls_ctr_drbg_seed()).
+ *
+ * Note that the value of #MBEDTLS_CTR_DRBG_ENTROPY_LEN defaults to:
+ * - \c 48 if the module \c MBEDTLS_SHA512_C is enabled and the symbol
+ *   \c MBEDTLS_ENTROPY_FORCE_SHA256 is not enabled at compile time.
+ *   This is the default configuration of the library.
+ * - \c 32 if the module \c MBEDTLS_SHA512_C is disabled at compile time.
+ * - \c 32 if \c MBEDTLS_ENTROPY_FORCE_SHA256 is enabled at compile time.
  */
 /*
- *  Copyright (C) 2006-2018, Arm Limited (or its affiliates), All Rights Reserved
+ *  Copyright (C) 2006-2019, Arm Limited (or its affiliates), All Rights Reserved
  *  SPDX-License-Identifier: GPL-2.0
  *
  *  This program is free software; you can redistribute it and/or modify
@@ -61,21 +86,29 @@
  * \{
  */
 
+/** \def MBEDTLS_CTR_DRBG_ENTROPY_LEN
+ *
+ * \brief The amount of entropy used per seed by default, in bytes.
+ */
 #if !defined(MBEDTLS_CTR_DRBG_ENTROPY_LEN)
 #if defined(MBEDTLS_SHA512_C) && !defined(MBEDTLS_ENTROPY_FORCE_SHA256)
+/** This is 48 bytes because the entropy module uses SHA-512
+ * (\c MBEDTLS_ENTROPY_FORCE_SHA256 is not set).
+ */
 #define MBEDTLS_CTR_DRBG_ENTROPY_LEN        48
-/**< The amount of entropy used per seed by default:
- * <ul><li>48 with SHA-512.</li>
- * <li>32 with SHA-256.</li></ul>
+
+#else /* defined(MBEDTLS_SHA512_C) && !defined(MBEDTLS_ENTROPY_FORCE_SHA256) */
+
+/** This is 32 bytes because the entropy module uses SHA-256
+ * (the SHA512 module is disabled or
+ * \c MBEDTLS_ENTROPY_FORCE_SHA256 is enabled).
+ *
+ * \warning To achieve a 256-bit security strength, you must pass a nonce
+ *           to mbedtls_ctr_drbg_seed().
  */
-#else
 #define MBEDTLS_CTR_DRBG_ENTROPY_LEN        32
-/**< Amount of entropy used per seed by default:
- * <ul><li>48 with SHA-512.</li>
- * <li>32 with SHA-256.</li></ul>
- */
-#endif
-#endif
+#endif /* defined(MBEDTLS_SHA512_C) && !defined(MBEDTLS_ENTROPY_FORCE_SHA256) */
+#endif /* !defined(MBEDTLS_CTR_DRBG_ENTROPY_LEN) */
 
 #if !defined(MBEDTLS_CTR_DRBG_RESEED_INTERVAL)
 #define MBEDTLS_CTR_DRBG_RESEED_INTERVAL    10000
@@ -94,7 +127,7 @@
 
 #if !defined(MBEDTLS_CTR_DRBG_MAX_SEED_INPUT)
 #define MBEDTLS_CTR_DRBG_MAX_SEED_INPUT     384
-/**< The maximum size of seed or reseed buffer. */
+/**< The maximum size of seed or reseed buffer in bytes. */
 #endif
 
 /* \} name SECTION: Module settings */
@@ -152,17 +185,67 @@ void mbedtls_ctr_drbg_init( mbedtls_ctr_drbg_context *ctx );
  * \brief               This function seeds and sets up the CTR_DRBG
  *                      entropy source for future reseeds.
  *
- * \note Personalization data can be provided in addition to the more generic
- *       entropy source, to make this instantiation as unique as possible.
- *
+ * A typical choice for the \p f_entropy and \p p_entropy parameters is
+ * to use the entropy module:
+ * - \p f_entropy is mbedtls_entropy_func();
+ * - \p p_entropy is an instance of ::mbedtls_entropy_context initialized
+ *   with mbedtls_entropy_init() (which registers the platform's default
+ *   entropy sources).
+ *
+ * The entropy length is #MBEDTLS_CTR_DRBG_ENTROPY_LEN by default.
+ * You can override it by calling mbedtls_ctr_drbg_set_entropy_len().
+ *
+ * You can provide a personalization string in addition to the
+ * entropy source, to make this instantiation as unique as possible.
+ *
+ * \note                The _seed_material_ value passed to the derivation
+ *                      function in the CTR_DRBG Instantiate Process
+ *                      described in NIST SP 800-90A §10.2.1.3.2
+ *                      is the concatenation of the string obtained from
+ *                      calling \p f_entropy and the \p custom string.
+ *                      The origin of the nonce depends on the value of
+ *                      the entropy length relative to the security strength.
+ *                      - If the entropy length is at least 1.5 times the
+ *                        security strength then the nonce is taken from the
+ *                        string obtained with \p f_entropy.
+ *                      - If the entropy length is less than the security
+ *                        strength, then the nonce is taken from \p custom.
+ *                        In this case, for compliance with SP 800-90A,
+ *                        you must pass a unique value of \p custom at
+ *                        each invocation. See SP 800-90A §8.6.7 for more
+ *                        details.
+ */
+#if MBEDTLS_CTR_DRBG_ENTROPY_LEN < MBEDTLS_CTR_DRBG_KEYSIZE * 3 / 2
+/** \warning            When #MBEDTLS_CTR_DRBG_ENTROPY_LEN is less than
+ *                      48, to achieve a 256-bit security strength,
+ *                      you must pass a value of \p custom that is a nonce:
+ *                      this value must never be repeated in subsequent
+ *                      runs of the same application or on a different
+ *                      device.
+ */
+#endif
+/**
  * \param ctx           The CTR_DRBG context to seed.
+ *                      It must have been initialized with
+ *                      mbedtls_ctr_drbg_init().
+ *                      After a successful call to mbedtls_ctr_drbg_seed(),
+ *                      you may not call mbedtls_ctr_drbg_seed() again on
+ *                      the same context unless you call
+ *                      mbedtls_ctr_drbg_free() and mbedtls_ctr_drbg_init()
+ *                      again first.
  * \param f_entropy     The entropy callback, taking as arguments the
  *                      \p p_entropy context, the buffer to fill, and the
-                        length of the buffer.
- * \param p_entropy     The entropy context.
- * \param custom        Personalization data, that is device-specific
-                        identifiers. Can be NULL.
- * \param len           The length of the personalization data.
+ *                      length of the buffer.
+ *                      \p f_entropy is always called with a buffer size
+ *                      equal to the entropy length.
+ * \param p_entropy     The entropy context to pass to \p f_entropy.
+ * \param custom        The personalization string.
+ *                      This can be \c NULL, in which case the personalization
+ *                      string is empty regardless of the value of \p len.
+ * \param len           The length of the personalization string.
+ *                      This must be at most
+ *                      #MBEDTLS_CTR_DRBG_MAX_SEED_INPUT
+ *                      - #MBEDTLS_CTR_DRBG_ENTROPY_LEN.
  *
  * \return              \c 0 on success, or
  *                      #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED on failure.
@@ -185,7 +268,8 @@ void mbedtls_ctr_drbg_free( mbedtls_ctr_drbg_context *ctx );
  *                      The default value is off.
  *
  * \note                If enabled, entropy is gathered at the beginning of
- *                      every call to mbedtls_ctr_drbg_random_with_add().
+ *                      every call to mbedtls_ctr_drbg_random_with_add()
+ *                      or mbedtls_ctr_drbg_random().
  *                      Only use this if your entropy source has sufficient
  *                      throughput.
  *
@@ -197,18 +281,29 @@ void mbedtls_ctr_drbg_set_prediction_resistance(
mbedtls_ctr_drbg_context *ctx,
 
 /**
  * \brief               This function sets the amount of entropy grabbed on each
- *                      seed or reseed. The default value is
- *                      #MBEDTLS_CTR_DRBG_ENTROPY_LEN.
+ *                      seed or reseed.
+ *
+ * The default value is #MBEDTLS_CTR_DRBG_ENTROPY_LEN.
+ *
+ * \note                The security strength of CTR_DRBG is bounded by the
+ *                      entropy length. Thus \p len must be at least
+ *                      32 (in bytes) to achieve a 256-bit strength.
  *
  * \param ctx           The CTR_DRBG context.
- * \param len           The amount of entropy to grab.
+ * \param len           The amount of entropy to grab, in bytes.
+ *                      This must be at most #MBEDTLS_CTR_DRBG_MAX_SEED_INPUT.
  */
 void mbedtls_ctr_drbg_set_entropy_len( mbedtls_ctr_drbg_context *ctx,
                                size_t len );
 
 /**
  * \brief               This function sets the reseed interval.
- *                      The default value is #MBEDTLS_CTR_DRBG_RESEED_INTERVAL.
+ *
+ * The reseed interval is the number of calls to mbedtls_ctr_drbg_random()
+ * or mbedtls_ctr_drbg_random_with_add() after which the entropy function
+ * is called again.
+ *
+ * The default value is #MBEDTLS_CTR_DRBG_RESEED_INTERVAL.
  *
  * \param ctx           The CTR_DRBG context.
  * \param interval      The reseed interval.
@@ -221,8 +316,12 @@ void mbedtls_ctr_drbg_set_reseed_interval( mbedtls_ctr_drbg_context
*ctx,
  *                      extracts data from the entropy source.
  *
  * \param ctx           The CTR_DRBG context.
- * \param additional    Additional data to add to the state. Can be NULL.
+ * \param additional    Additional data to add to the state. Can be \c NULL.
  * \param len           The length of the additional data.
+ *                      This must be less than
+ *                      #MBEDTLS_CTR_DRBG_MAX_SEED_INPUT - \c entropy_len
+ *                      where \c entropy_len is the entropy length
+ *                      configured for the context.
  *
  * \return   \c 0 on success, or
  *           #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED on failure.
@@ -234,7 +333,8 @@ int mbedtls_ctr_drbg_reseed( mbedtls_ctr_drbg_context *ctx,
  * \brief               This function updates the state of the CTR_DRBG context.
  *
  * \param ctx           The CTR_DRBG context.
- * \param additional    The data to update the state with.
+ * \param additional    The data to update the state with. This must not be
+ *                      \c NULL unless \p add_len is \c 0.
  * \param add_len       Length of \p additional in bytes. This must be at
  *                      most #MBEDTLS_CTR_DRBG_MAX_SEED_INPUT.
  *
@@ -260,8 +360,10 @@ int mbedtls_ctr_drbg_update_ret( mbedtls_ctr_drbg_context *ctx,
  *                      The remaining Bytes are silently discarded.
  *
  * \param ctx           The CTR_DRBG context.
- * \param additional    The data to update the state with.
- * \param add_len       Length of \p additional data.
+ * \param additional    The data to update the state with. This must not be
+ *                      \c NULL unless \p add_len is \c 0.
+ * \param add_len       Length of \p additional data. This must be at
+ *                      most #MBEDTLS_CTR_DRBG_MAX_SEED_INPUT.
  */
 void mbedtls_ctr_drbg_update( mbedtls_ctr_drbg_context *ctx,
                               const unsigned char *additional,
@@ -271,17 +373,26 @@ void mbedtls_ctr_drbg_update( mbedtls_ctr_drbg_context *ctx,
  * \brief   This function updates a CTR_DRBG instance with additional
  *          data and uses it to generate random data.
  *
- * \note    The function automatically reseeds if the reseed counter is exceeded.
+ * This function automatically reseeds if the reseed counter is exceeded
+ * or prediction resistance is enabled.
  *
  * \param p_rng         The CTR_DRBG context. This must be a pointer to a
  *                      #mbedtls_ctr_drbg_context structure.
  * \param output        The buffer to fill.
- * \param output_len    The length of the buffer.
- * \param additional    Additional data to update. Can be NULL.
- * \param add_len       The length of the additional data.
- *
- * \return    \c 0 on success, or
- *            #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED or
+ * \param output_len    The length of the buffer in bytes.
+ * \param additional    Additional data to update. Can be \c NULL, in which
+ *                      case the additional data is empty regardless of
+ *                      the value of \p add_len.
+ * \param add_len       The length of the additional data
+ *                      if \p additional is not \c NULL.
+ *                      This must be less than #MBEDTLS_CTR_DRBG_MAX_INPUT
+ *                      and less than
+ *                      #MBEDTLS_CTR_DRBG_MAX_SEED_INPUT - \c entropy_len
+ *                      where \c entropy_len is the entropy length
+ *                      configured for the context.
+ *
+ * \return    \c 0 on success.
+ * \return    #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED or
  *            #MBEDTLS_ERR_CTR_DRBG_REQUEST_TOO_BIG on failure.
  */
 int mbedtls_ctr_drbg_random_with_add( void *p_rng,
@@ -291,15 +402,17 @@ int mbedtls_ctr_drbg_random_with_add( void *p_rng,
 /**
  * \brief   This function uses CTR_DRBG to generate random data.
  *
- * \note    The function automatically reseeds if the reseed counter is exceeded.
+ * This function automatically reseeds if the reseed counter is exceeded
+ * or prediction resistance is enabled.
+ *
  *
  * \param p_rng         The CTR_DRBG context. This must be a pointer to a
  *                      #mbedtls_ctr_drbg_context structure.
  * \param output        The buffer to fill.
- * \param output_len    The length of the buffer.
+ * \param output_len    The length of the buffer in bytes.
  *
- * \return              \c 0 on success, or
- *                      #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED or
+ * \return              \c 0 on success.
+ * \return              #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED or
  *                      #MBEDTLS_ERR_CTR_DRBG_REQUEST_TOO_BIG on failure.
  */
 int mbedtls_ctr_drbg_random( void *p_rng,
@@ -312,9 +425,9 @@ int mbedtls_ctr_drbg_random( void *p_rng,
  * \param ctx           The CTR_DRBG context.
  * \param path          The name of the file.
  *
- * \return              \c 0 on success,
- *                      #MBEDTLS_ERR_CTR_DRBG_FILE_IO_ERROR on file error, or
- *                      #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED on
+ * \return              \c 0 on success.
+ * \return              #MBEDTLS_ERR_CTR_DRBG_FILE_IO_ERROR on file error.
+ * \return              #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED on reseed
  *                      failure.
  */
 int mbedtls_ctr_drbg_write_seed_file( mbedtls_ctr_drbg_context *ctx, const char *path );
@@ -326,10 +439,12 @@ int mbedtls_ctr_drbg_write_seed_file( mbedtls_ctr_drbg_context *ctx,
const char
  * \param ctx           The CTR_DRBG context.
  * \param path          The name of the file.
  *
- * \return              \c 0 on success,
- *                      #MBEDTLS_ERR_CTR_DRBG_FILE_IO_ERROR on file error,
- *                      #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED or
- *                      #MBEDTLS_ERR_CTR_DRBG_INPUT_TOO_BIG on failure.
+ * \return              \c 0 on success.
+ * \return              #MBEDTLS_ERR_CTR_DRBG_FILE_IO_ERROR on file error.
+ * \return              #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED on
+ *                      reseed failure.
+ * \return              #MBEDTLS_ERR_CTR_DRBG_INPUT_TOO_BIG if the existing
+ *                      seed file is too large.
  */
 int mbedtls_ctr_drbg_update_seed_file( mbedtls_ctr_drbg_context *ctx, const char *path
);
 #endif /* MBEDTLS_FS_IO */
diff --git a/sdk/include/reactos/libs/mbedtls/hmac_drbg.h
b/sdk/include/reactos/libs/mbedtls/hmac_drbg.h
index 6085d476f09..03939759c6a 100644
--- a/sdk/include/reactos/libs/mbedtls/hmac_drbg.h
+++ b/sdk/include/reactos/libs/mbedtls/hmac_drbg.h
@@ -1,10 +1,14 @@
 /**
  * \file hmac_drbg.h
  *
- * \brief HMAC_DRBG (NIST SP 800-90A)
+ * \brief The HMAC_DRBG pseudorandom generator.
+ *
+ * This module implements the HMAC_DRBG pseudorandom generator described
+ * in <em>NIST SP 800-90A: Recommendation for Random Number Generation Using
+ * Deterministic Random Bit Generators</em>.
  */
 /*
- *  Copyright (C) 2006-2015, ARM Limited, All Rights Reserved
+ *  Copyright (C) 2006-2019, ARM Limited, All Rights Reserved
  *  SPDX-License-Identifier: GPL-2.0
  *
  *  This program is free software; you can redistribute it and/or modify
@@ -106,38 +110,72 @@ typedef struct
 } mbedtls_hmac_drbg_context;
 
 /**
- * \brief               HMAC_DRBG context initialization
- *                      Makes the context ready for mbedtls_hmac_drbg_seed(),
- *                      mbedtls_hmac_drbg_seed_buf() or
- *                      mbedtls_hmac_drbg_free().
+ * \brief               HMAC_DRBG context initialization.
+ *
+ * This function makes the context ready for mbedtls_hmac_drbg_seed(),
+ * mbedtls_hmac_drbg_seed_buf() or mbedtls_hmac_drbg_free().
  *
- * \param ctx           HMAC_DRBG context to be initialized
+ * \param ctx           HMAC_DRBG context to be initialized.
  */
 void mbedtls_hmac_drbg_init( mbedtls_hmac_drbg_context *ctx );
 
 /**
- * \brief               HMAC_DRBG initial seeding
- *                      Seed and setup entropy source for future reseeds.
- *
- * \param ctx           HMAC_DRBG context to be seeded
- * \param md_info       MD algorithm to use for HMAC_DRBG
- * \param f_entropy     Entropy callback (p_entropy, buffer to fill, buffer
- *                      length)
- * \param p_entropy     Entropy context
- * \param custom        Personalization data (Device specific identifiers)
- *                      (Can be NULL)
- * \param len           Length of personalization data
- *
- * \note                The "security strength" as defined by NIST is set to:
- *                      128 bits if md_alg is SHA-1,
- *                      192 bits if md_alg is SHA-224,
- *                      256 bits if md_alg is SHA-256 or higher.
- *                      Note that SHA-256 is just as efficient as SHA-224.
+ * \brief               HMAC_DRBG initial seeding.
+ *
+ * Set the initial seed and set up the entropy source for future reseeds.
+ *
+ * A typical choice for the \p f_entropy and \p p_entropy parameters is
+ * to use the entropy module:
+ * - \p f_entropy is mbedtls_entropy_func();
+ * - \p p_entropy is an instance of ::mbedtls_entropy_context initialized
+ *   with mbedtls_entropy_init() (which registers the platform's default
+ *   entropy sources).
  *
- * \return              0 if successful, or
- *                      MBEDTLS_ERR_MD_BAD_INPUT_DATA, or
- *                      MBEDTLS_ERR_MD_ALLOC_FAILED, or
- *                      MBEDTLS_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED.
+ * You can provide a personalization string in addition to the
+ * entropy source, to make this instantiation as unique as possible.
+ *
+ * \note                By default, the security strength as defined by NIST is:
+ *                      - 128 bits if \p md_info is SHA-1;
+ *                      - 192 bits if \p md_info is SHA-224;
+ *                      - 256 bits if \p md_info is SHA-256, SHA-384 or SHA-512.
+ *                      Note that SHA-256 is just as efficient as SHA-224.
+ *                      The security strength can be reduced if a smaller
+ *                      entropy length is set with
+ *                      mbedtls_hmac_drbg_set_entropy_len().
+ *
+ * \note                The default entropy length is the security strength
+ *                      (converted from bits to bytes). You can override
+ *                      it by calling mbedtls_hmac_drbg_set_entropy_len().
+ *
+ * \note                During the initial seeding, this function calls
+ *                      the entropy source to obtain a nonce
+ *                      whose length is half the entropy length.
+ *
+ * \param ctx           HMAC_DRBG context to be seeded.
+ * \param md_info       MD algorithm to use for HMAC_DRBG.
+ * \param f_entropy     The entropy callback, taking as arguments the
+ *                      \p p_entropy context, the buffer to fill, and the
+ *                      length of the buffer.
+ *                      \p f_entropy is always called with a length that is
+ *                      less than or equal to the entropy length.
+ * \param p_entropy     The entropy context to pass to \p f_entropy.
+ * \param custom        The personalization string.
+ *                      This can be \c NULL, in which case the personalization
+ *                      string is empty regardless of the value of \p len.
+ * \param len           The length of the personalization string.
+ *                      This must be at most #MBEDTLS_HMAC_DRBG_MAX_INPUT
+ *                      and also at most
+ *                      #MBEDTLS_HMAC_DRBG_MAX_SEED_INPUT - \p entropy_len * 3 / 2
+ *                      where \p entropy_len is the entropy length
+ *                      described above.
+ *
+ * \return              \c 0 if successful.
+ * \return              #MBEDTLS_ERR_MD_BAD_INPUT_DATA if \p md_info is
+ *                      invalid.
+ * \return              #MBEDTLS_ERR_MD_ALLOC_FAILED if there was not enough
+ *                      memory to allocate context data.
+ * \return              #MBEDTLS_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED
+ *                      if the call to \p f_entropy failed.
  */
 int mbedtls_hmac_drbg_seed( mbedtls_hmac_drbg_context *ctx,
                     const mbedtls_md_info_t * md_info,
@@ -148,66 +186,80 @@ int mbedtls_hmac_drbg_seed( mbedtls_hmac_drbg_context *ctx,
 
 /**
  * \brief               Initilisation of simpified HMAC_DRBG (never reseeds).
- *                      (For use with deterministic ECDSA.)
  *
- * \param ctx           HMAC_DRBG context to be initialised
- * \param md_info       MD algorithm to use for HMAC_DRBG
- * \param data          Concatenation of entropy string and additional data
- * \param data_len      Length of data in bytes
+ * This function is meant for use in algorithms that need a pseudorandom
+ * input such as deterministic ECDSA.
  *
- * \return              0 if successful, or
- *                      MBEDTLS_ERR_MD_BAD_INPUT_DATA, or
- *                      MBEDTLS_ERR_MD_ALLOC_FAILED.
+ * \param ctx           HMAC_DRBG context to be initialised.
+ * \param md_info       MD algorithm to use for HMAC_DRBG.
+ * \param data          Concatenation of the initial entropy string and
+ *                      the additional data.
+ * \param data_len      Length of \p data in bytes.
+ *
+ * \return              \c 0 if successful. or
+ * \return              #MBEDTLS_ERR_MD_BAD_INPUT_DATA if \p md_info is
+ *                      invalid.
+ * \return              #MBEDTLS_ERR_MD_ALLOC_FAILED if there was not enough
+ *                      memory to allocate context data.
  */
 int mbedtls_hmac_drbg_seed_buf( mbedtls_hmac_drbg_context *ctx,
                         const mbedtls_md_info_t * md_info,
                         const unsigned char *data, size_t data_len );
 
 /**
- * \brief               Enable / disable prediction resistance (Default: Off)
+ * \brief               This function turns prediction resistance on or off.
+ *                      The default value is off.
  *
- * Note: If enabled, entropy is used for ctx->entropy_len before each call!
- *       Only use this if you have ample supply of good entropy!
+ * \note                If enabled, entropy is gathered at the beginning of
+ *                      every call to mbedtls_hmac_drbg_random_with_add()
+ *                      or mbedtls_hmac_drbg_random().
+ *                      Only use this if your entropy source has sufficient
+ *                      throughput.
  *
- * \param ctx           HMAC_DRBG context
- * \param resistance    MBEDTLS_HMAC_DRBG_PR_ON or MBEDTLS_HMAC_DRBG_PR_OFF
+ * \param ctx           The HMAC_DRBG context.
+ * \param resistance    #MBEDTLS_HMAC_DRBG_PR_ON or #MBEDTLS_HMAC_DRBG_PR_OFF.
  */
 void mbedtls_hmac_drbg_set_prediction_resistance( mbedtls_hmac_drbg_context *ctx,
                                           int resistance );
 
 /**
- * \brief               Set the amount of entropy grabbed on each reseed
- *                      (Default: given by the security strength, which
- *                      depends on the hash used, see \c mbedtls_hmac_drbg_init() )
+ * \brief               This function sets the amount of entropy grabbed on each
+ *                      seed or reseed.
  *
- * \param ctx           HMAC_DRBG context
- * \param len           Amount of entropy to grab, in bytes
+ * See the documentation of mbedtls_hmac_drbg_seed() for the default value.
+ *
+ * \param ctx           The HMAC_DRBG context.
+ * \param len           The amount of entropy to grab, in bytes.
  */
 void mbedtls_hmac_drbg_set_entropy_len( mbedtls_hmac_drbg_context *ctx,
                                 size_t len );
 
 /**
- * \brief               Set the reseed interval
- *                      (Default: MBEDTLS_HMAC_DRBG_RESEED_INTERVAL)
+ * \brief               Set the reseed interval.
  *
- * \param ctx           HMAC_DRBG context
- * \param interval      Reseed interval
+ * The reseed interval is the number of calls to mbedtls_hmac_drbg_random()
+ * or mbedtls_hmac_drbg_random_with_add() after which the entropy function
+ * is called again.
+ *
+ * The default value is #MBEDTLS_HMAC_DRBG_RESEED_INTERVAL.
+ *
+ * \param ctx           The HMAC_DRBG context.
+ * \param interval      The reseed interval.
  */
 void mbedtls_hmac_drbg_set_reseed_interval( mbedtls_hmac_drbg_context *ctx,
                                     int interval );
 
 /**
- * \brief               HMAC_DRBG update state
+ * \brief               This function updates the state of the HMAC_DRBG context.
  *
- * \param ctx           HMAC_DRBG context
- * \param additional    Additional data to update state with, or NULL
- * \param add_len       Length of additional data, or 0
+ * \param ctx           The HMAC_DRBG context.
+ * \param additional    The data to update the state with.
+ *                      If this is \c NULL, there is no additional data.
+ * \param add_len       Length of \p additional in bytes.
+ *                      Unused if \p additional is \c NULL.
  *
  * \return              \c 0 on success, or an error from the underlying
  *                      hash calculation.
- *
- * \note                Additional data is optional, pass NULL and 0 as second
- *                      third argument if no additional data is being used.
  */
 int mbedtls_hmac_drbg_update_ret( mbedtls_hmac_drbg_context *ctx,
                        const unsigned char *additional, size_t add_len );
@@ -230,33 +282,52 @@ void mbedtls_hmac_drbg_update( mbedtls_hmac_drbg_context *ctx,
                                size_t add_len );
 
 /**
- * \brief               HMAC_DRBG reseeding (extracts data from entropy source)
- *
- * \param ctx           HMAC_DRBG context
- * \param additional    Additional data to add to state (Can be NULL)
- * \param len           Length of additional data
- *
- * \return              0 if successful, or
- *                      MBEDTLS_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED
+ * \brief               This function reseeds the HMAC_DRBG context, that is
+ *                      extracts data from the entropy source.
+ *
+ * \param ctx           The HMAC_DRBG context.
+ * \param additional    Additional data to add to the state.
+ *                      If this is \c NULL, there is no additional data
+ *                      and \p len should be \c 0.
+ * \param len           The length of the additional data.
+ *                      This must be at most #MBEDTLS_HMAC_DRBG_MAX_INPUT
+ *                      and also at most
+ *                      #MBEDTLS_HMAC_DRBG_MAX_SEED_INPUT - \p entropy_len
+ *                      where \p entropy_len is the entropy length
+ *                      (see mbedtls_hmac_drbg_set_entropy_len()).
+ *
+ * \return              \c 0 if successful.
+ * \return              #MBEDTLS_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED
+ *                      if a call to the entropy function failed.
  */
 int mbedtls_hmac_drbg_reseed( mbedtls_hmac_drbg_context *ctx,
                       const unsigned char *additional, size_t len );
 
 /**
- * \brief               HMAC_DRBG generate random with additional update input
- *
- * Note: Automatically reseeds if reseed_counter is reached or PR is enabled.
- *
- * \param p_rng         HMAC_DRBG context
- * \param output        Buffer to fill
- * \param output_len    Length of the buffer
- * \param additional    Additional data to update with (can be NULL)
- * \param add_len       Length of additional data (can be 0)
- *
- * \return              0 if successful, or
- *                      MBEDTLS_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED, or
- *                      MBEDTLS_ERR_HMAC_DRBG_REQUEST_TOO_BIG, or
- *                      MBEDTLS_ERR_HMAC_DRBG_INPUT_TOO_BIG.
+ * \brief   This function updates an HMAC_DRBG instance with additional
+ *          data and uses it to generate random data.
+ *
+ * This function automatically reseeds if the reseed counter is exceeded
+ * or prediction resistance is enabled.
+ *
+ * \param p_rng         The HMAC_DRBG context. This must be a pointer to a
+ *                      #mbedtls_hmac_drbg_context structure.
+ * \param output        The buffer to fill.
+ * \param output_len    The length of the buffer in bytes.
+ *                      This must be at most #MBEDTLS_HMAC_DRBG_MAX_REQUEST.
+ * \param additional    Additional data to update with.
+ *                      If this is \c NULL, there is no additional data
+ *                      and \p add_len should be \c 0.
+ * \param add_len       The length of the additional data.
+ *                      This must be at most #MBEDTLS_HMAC_DRBG_MAX_INPUT.
+ *
+ * \return              \c 0 if successful.
+ * \return              #MBEDTLS_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED
+ *                      if a call to the entropy source failed.
+ * \return              #MBEDTLS_ERR_HMAC_DRBG_REQUEST_TOO_BIG if
+ *                      \p output_len > #MBEDTLS_HMAC_DRBG_MAX_REQUEST.
+ * \return              #MBEDTLS_ERR_HMAC_DRBG_INPUT_TOO_BIG if
+ *                      \p add_len > #MBEDTLS_HMAC_DRBG_MAX_INPUT.
  */
 int mbedtls_hmac_drbg_random_with_add( void *p_rng,
                                unsigned char *output, size_t output_len,
@@ -264,49 +335,59 @@ int mbedtls_hmac_drbg_random_with_add( void *p_rng,
                                size_t add_len );
 
 /**
- * \brief               HMAC_DRBG generate random
- *
- * Note: Automatically reseeds if reseed_counter is reached or PR is enabled.
- *
- * \param p_rng         HMAC_DRBG context
- * \param output        Buffer to fill
- * \param out_len       Length of the buffer
- *
- * \return              0 if successful, or
- *                      MBEDTLS_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED, or
- *                      MBEDTLS_ERR_HMAC_DRBG_REQUEST_TOO_BIG
+ * \brief   This function uses HMAC_DRBG to generate random data.
+ *
+ * This function automatically reseeds if the reseed counter is exceeded
+ * or prediction resistance is enabled.
+ *
+ * \param p_rng         The HMAC_DRBG context. This must be a pointer to a
+ *                      #mbedtls_hmac_drbg_context structure.
+ * \param output        The buffer to fill.
+ * \param out_len       The length of the buffer in bytes.
+ *                      This must be at most #MBEDTLS_HMAC_DRBG_MAX_REQUEST.
+ *
+ * \return              \c 0 if successful.
+ * \return              #MBEDTLS_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED
+ *                      if a call to the entropy source failed.
+ * \return              #MBEDTLS_ERR_HMAC_DRBG_REQUEST_TOO_BIG if
+ *                      \p out_len > #MBEDTLS_HMAC_DRBG_MAX_REQUEST.
  */
 int mbedtls_hmac_drbg_random( void *p_rng, unsigned char *output, size_t out_len );
 
 /**
  * \brief               Free an HMAC_DRBG context
  *
- * \param ctx           HMAC_DRBG context to free.
+ * \param ctx           The HMAC_DRBG context to free.
  */
 void mbedtls_hmac_drbg_free( mbedtls_hmac_drbg_context *ctx );
 
 #if defined(MBEDTLS_FS_IO)
 /**
- * \brief               Write a seed file
+ * \brief               This function writes a seed file.
  *
- * \param ctx           HMAC_DRBG context
- * \param path          Name of the file
+ * \param ctx           The HMAC_DRBG context.
+ * \param path          The name of the file.
  *
- * \return              0 if successful, 1 on file error, or
- *                      MBEDTLS_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED
+ * \return              \c 0 on success.
+ * \return              #MBEDTLS_ERR_HMAC_DRBG_FILE_IO_ERROR on file error.
+ * \return              #MBEDTLS_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED on reseed
+ *                      failure.
  */
 int mbedtls_hmac_drbg_write_seed_file( mbedtls_hmac_drbg_context *ctx, const char *path
);
 
 /**
- * \brief               Read and update a seed file. Seed is added to this
- *                      instance
- *
- * \param ctx           HMAC_DRBG context
- * \param path          Name of the file
- *
- * \return              0 if successful, 1 on file error,
- *                      MBEDTLS_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED or
- *                      MBEDTLS_ERR_HMAC_DRBG_INPUT_TOO_BIG
+ * \brief               This function reads and updates a seed file. The seed
+ *                      is added to this instance.
+ *
+ * \param ctx           The HMAC_DRBG context.
+ * \param path          The name of the file.
+ *
+ * \return              \c 0 on success.
+ * \return              #MBEDTLS_ERR_HMAC_DRBG_FILE_IO_ERROR on file error.
+ * \return              #MBEDTLS_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED on
+ *                      reseed failure.
+ * \return              #MBEDTLS_ERR_HMAC_DRBG_INPUT_TOO_BIG if the existing
+ *                      seed file is too large.
  */
 int mbedtls_hmac_drbg_update_seed_file( mbedtls_hmac_drbg_context *ctx, const char *path
);
 #endif /* MBEDTLS_FS_IO */
@@ -314,9 +395,10 @@ int mbedtls_hmac_drbg_update_seed_file( mbedtls_hmac_drbg_context
*ctx, const ch
 
 #if defined(MBEDTLS_SELF_TEST)
 /**
- * \brief               Checkup routine
+ * \brief               The HMAC_DRBG Checkup routine.
  *
- * \return              0 if successful, or 1 if the test failed
+ * \return              \c 0 if successful.
+ * \return              \c 1 if the test failed.
  */
 int mbedtls_hmac_drbg_self_test( int verbose );
 #endif