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Merge pull request #238 from hanno-arm/hmac_drbg_entropy_incompatibility_fix-crypto

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HMAC DRBG: Split entropy-gathering requests to reduce request sizes
This commit is contained in:
Jaeden Amero 2019-08-30 12:15:16 +01:00 committed by GitHub
commit 822b8f65bd
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GPG Key ID: 4AEE18F83AFDEB23
1 changed files with 64 additions and 22 deletions
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76
library/hmac_drbg.c
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@ -149,30 +149,65 @@ int mbedtls_hmac_drbg_seed_buf( mbedtls_hmac_drbg_context *ctx,
}
/*
* HMAC_DRBG reseeding: 10.1.2.4 (arabic) + 9.2 (Roman)
* Internal function used both for seeding and reseeding the DRBG.
* Comments starting with arabic numbers refer to section 10.1.2.4
* of SP800-90A, while roman numbers refer to section 9.2.
*/
int mbedtls_hmac_drbg_reseed( mbedtls_hmac_drbg_context *ctx,
const unsigned char *additional, size_t len )
static int hmac_drbg_reseed_core( mbedtls_hmac_drbg_context *ctx,
const unsigned char *additional, size_t len,
int use_nonce )
{
unsigned char seed[MBEDTLS_HMAC_DRBG_MAX_SEED_INPUT];
size_t seedlen;
size_t seedlen = 0;
int ret;
{
size_t total_entropy_len;
if( use_nonce == 0 )
total_entropy_len = ctx->entropy_len;
else
total_entropy_len = ctx->entropy_len * 3 / 2;
/* III. Check input length */
if( len > MBEDTLS_HMAC_DRBG_MAX_INPUT ||
ctx->entropy_len + len > MBEDTLS_HMAC_DRBG_MAX_SEED_INPUT )
total_entropy_len + len > MBEDTLS_HMAC_DRBG_MAX_SEED_INPUT )
{
return( MBEDTLS_ERR_HMAC_DRBG_INPUT_TOO_BIG );
}
}
memset( seed, 0, MBEDTLS_HMAC_DRBG_MAX_SEED_INPUT );
/* IV. Gather entropy_len bytes of entropy for the seed */
if( ( ret = ctx->f_entropy( ctx->p_entropy,
seed, ctx->entropy_len ) ) != 0 )
{
return( MBEDTLS_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED );
}
seedlen += ctx->entropy_len;
/* For initial seeding, allow adding of nonce generated
* from the entropy source. See Sect 8.6.7 in SP800-90A. */
if( use_nonce )
{
/* Note: We don't merge the two calls to f_entropy() in order
* to avoid requesting too much entropy from f_entropy()
* at once. Specifically, if the underlying digest is not
* SHA-1, 3 / 2 * entropy_len is at least 36 Bytes, which
* is larger than the maximum of 32 Bytes that our own
* entropy source implementation can emit in a single
* call in configurations disabling SHA-512. */
if( ( ret = ctx->f_entropy( ctx->p_entropy,
seed + seedlen,
ctx->entropy_len / 2 ) ) != 0 )
{
return( MBEDTLS_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED );
}
seedlen += ctx->entropy_len / 2;
}
seedlen = ctx->entropy_len;
/* 1. Concatenate entropy and additional data if any */
if( additional != NULL && len != 0 )
@ -194,8 +229,20 @@ exit:
return( ret );
}
/*
* HMAC_DRBG reseeding: 10.1.2.4 + 9.2
*/
int mbedtls_hmac_drbg_reseed( mbedtls_hmac_drbg_context *ctx,
const unsigned char *additional, size_t len )
{
return( hmac_drbg_reseed_core( ctx, additional, len, 0 ) );
}
/*
* HMAC_DRBG initialisation (10.1.2.3 + 9.1)
*
* The nonce is not passed as a separate parameter but extracted
* from the entropy source as suggested in 8.6.7.
*/
int mbedtls_hmac_drbg_seed( mbedtls_hmac_drbg_context *ctx,
const mbedtls_md_info_t * md_info,
@ -205,7 +252,7 @@ int mbedtls_hmac_drbg_seed( mbedtls_hmac_drbg_context *ctx,
size_t len )
{
int ret;
size_t entropy_len, md_size;
size_t md_size;
if( ( ret = mbedtls_md_setup( &ctx->md_ctx, md_info, 1 ) ) != 0 )
return( ret );
@ -233,20 +280,15 @@ int mbedtls_hmac_drbg_seed( mbedtls_hmac_drbg_context *ctx,
*
* (This also matches the sizes used in the NIST test vectors.)
*/
entropy_len = md_size <= 20 ? 16 : /* 160-bits hash -> 128 bits */
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 */
/*
* For initialisation, use more entropy to emulate a nonce
* (Again, matches test vectors.)
*/
ctx->entropy_len = entropy_len * 3 / 2;
if( ( ret = mbedtls_hmac_drbg_reseed( ctx, custom, len ) ) != 0 )
if( ( ret = hmac_drbg_reseed_core( ctx, custom, len,
1 /* add nonce */ ) ) != 0 )
{
return( ret );
ctx->entropy_len = entropy_len;
}
return( 0 );
}