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Integrated feedback of first code review

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- Fixed code style.
- Clarified the documentation of what happens when saltlen is set to
  MBEDTLS_RSA_SALT_LEN_ANY.
- Added range check on saltlen to reject out of range values.

(Code review done by @gilles-peskine-arm)

Signed-off-by: Cédric Meuter <cedric.meuter@gmail.com>
This commit is contained in:
Cédric Meuter 2020-04-25 09:24:11 +02:00
parent 8aa4d75ec9
commit 010ddc2b62
2 changed files with 17 additions and 13 deletions
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19
include/mbedtls/rsa.h
View file

@ -979,14 +979,11 @@ int mbedtls_rsa_rsassa_pkcs1_v15_sign( mbedtls_rsa_context *ctx,
* Specifications</em> it is advised to keep both hashes the
* same.
*
* \note This function always uses the maximum possible salt size,
* up to the length of the payload hash. This choice of salt
* size complies with FIPS 186-4 §5.5 (e) and RFC 8017 (PKCS#1
* v2.2) §9.1.1 step 3. Furthermore this function enforces a
* minimum salt size which is the hash size minus 2 bytes. If
* this minimum size is too large given the key size (the salt
* size, plus the hash size, plus 2 bytes must be no more than
* the key size in bytes), this function returns
* \note This function enforces that the provided salt length complies
* with FIPS 186-4 §5.5 (e) and RFC 8017 (PKCS#1 v2.2) §9.1.1
* step 3. The constraint is that the hash length plus the salt
* length plus 2 bytes must be at most the key length. If this
* constraint is not met, this function returns
* #MBEDTLS_ERR_RSA_BAD_INPUT_DATA.
*
* \deprecated It is deprecated and discouraged to call this function
@ -1014,8 +1011,10 @@ int mbedtls_rsa_rsassa_pkcs1_v15_sign( mbedtls_rsa_context *ctx,
* #MBEDTLS_MD_NONE, it must be a readable buffer of length
* the size of the hash corresponding to \p md_alg.
* \param saltlen The length of the salt that should be used.
* If passed MBEDTLS_RSA_SALT_LEN_ANY, the function will use
* the largest possible salt length.
* If passed #MBEDTLS_RSA_SALT_LEN_ANY, the function will use
* the largest possible salt length up to the hash length,
* which is the largest permitted by some standards including
* FIPS 186-4 §5.5.
* \param sig The buffer to hold the signature. This must be a writable
* buffer of length \c ctx->len Bytes. For example, \c 256 Bytes
* for an 2048-bit RSA modulus. A buffer length of

11
library/rsa.c
View file

@ -1843,8 +1843,9 @@ int mbedtls_rsa_rsassa_pss_sign_ext( mbedtls_rsa_context *ctx,
if (saltlen == MBEDTLS_RSA_SALT_LEN_ANY)
{
/* Calculate the largest possible salt length. Normally this is the hash
* length, which is the maximum length the salt can have. If there is not
/* Calculate the largest possible salt length, up to the hash size.
* Normally this is the hash length, which is the maximum salt length
* according to FIPS 185-4 §5.5 (e) and common practice. If there is not
* enough room, use the maximum salt length that fits. The constraint is
* that the hash length plus the salt length plus 2 bytes must be at most
* the key length. This complies with FIPS 186-4 §5.5 (e) and RFC 8017
@ -1857,9 +1858,13 @@ int mbedtls_rsa_rsassa_pss_sign_ext( mbedtls_rsa_context *ctx,
else
slen = olen - hlen - 2;
}
else if ( (saltlen < 0) || ((size_t) saltlen > olen - hlen - 2) )
{
return( MBEDTLS_ERR_RSA_BAD_INPUT_DATA );
}
else
{
slen = (size_t)saltlen;
slen = (size_t) saltlen;
}
memset( sig, 0, olen );