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Verify PKCS1 v1.5 signature without parsing

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This commit modifies the PKCS1 v1.5 signature verification function `mbedtls_rsa_rsassa_pkcs1_v15_verify` to prepare the
expected PKCS1-v1.5-encoded hash using the function also used by the signing routine `mbedtls_rsa_rsassa_pkcs1_v15_sign`
and comparing it to the provided byte-string afterwards. This comes at the benefits of (1) avoiding any error-prone
parsing, (2) removing the dependency of the RSA module on the ASN.1 parsing module, and (3) reducing code size.
This commit is contained in:
Hanno Becker 2017-09-06 12:39:49 +01:00
parent fdf38030de
commit 64a8c0acd6
1 changed files with 42 additions and 99 deletions
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155
library/rsa.c
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@ -1559,121 +1559,64 @@ int mbedtls_rsa_rsassa_pkcs1_v15_verify( mbedtls_rsa_context *ctx,
const unsigned char *hash,
const unsigned char *sig )
{
int ret;
size_t len, siglen, asn1_len;
unsigned char *p, *p0, *end;
mbedtls_md_type_t msg_md_alg;
const mbedtls_md_info_t *md_info;
mbedtls_asn1_buf oid;
unsigned char buf[MBEDTLS_MPI_MAX_SIZE];
int ret = 0;
const size_t sig_len = ctx->len;
unsigned char *encoded = NULL, *encoded_expected = NULL;
if( mode == MBEDTLS_RSA_PRIVATE && ctx->padding != MBEDTLS_RSA_PKCS_V15 )
return( MBEDTLS_ERR_RSA_BAD_INPUT_DATA );
siglen = ctx->len;
/*
* Prepare expected PKCS1 v1.5 encoding of hash.
*/
if( siglen < 16 || siglen > sizeof( buf ) )
return( MBEDTLS_ERR_RSA_BAD_INPUT_DATA );
if( ( encoded = mbedtls_calloc( 1, sig_len ) ) == NULL ||
( encoded_expected = mbedtls_calloc( 1, sig_len ) ) == NULL )
{
ret = MBEDTLS_ERR_MPI_ALLOC_FAILED;
goto cleanup;
}
if( ( ret = rsa_rsassa_pkcs1_v15_encode( md_alg, hashlen, hash, sig_len,
encoded_expected ) ) != 0 )
goto cleanup;
/*
* Apply RSA primitive to get what should be PKCS1 encoded hash.
*/
ret = ( mode == MBEDTLS_RSA_PUBLIC )
? mbedtls_rsa_public( ctx, sig, buf )
: mbedtls_rsa_private( ctx, f_rng, p_rng, sig, buf );
? mbedtls_rsa_public( ctx, sig, encoded )
: mbedtls_rsa_private( ctx, f_rng, p_rng, sig, encoded );
if( ret != 0 )
goto cleanup;
/*
* Compare
*/
if( ( ret = mbedtls_safer_memcmp( encoded, encoded_expected,
sig_len ) ) != 0 )
{
ret = MBEDTLS_ERR_RSA_VERIFY_FAILED;
goto cleanup;
}
cleanup:
if( encoded != NULL )
{
mbedtls_zeroize( encoded, sig_len );
mbedtls_free( encoded );
}
if( encoded_expected != NULL )
{
mbedtls_zeroize( encoded_expected, sig_len );
mbedtls_free( encoded_expected );
}
return( ret );
p = buf;
if( *p++ != 0 || *p++ != MBEDTLS_RSA_SIGN )
return( MBEDTLS_ERR_RSA_INVALID_PADDING );
while( *p != 0 )
{
if( p >= buf + siglen - 1 || *p != 0xFF )
return( MBEDTLS_ERR_RSA_INVALID_PADDING );
p++;
}
p++; /* skip 00 byte */
/* We've read: 00 01 PS 00 where PS must be at least 8 bytes */
if( p - buf < 11 )
return( MBEDTLS_ERR_RSA_INVALID_PADDING );
len = siglen - ( p - buf );
if( len == hashlen && md_alg == MBEDTLS_MD_NONE )
{
if( memcmp( p, hash, hashlen ) == 0 )
return( 0 );
else
return( MBEDTLS_ERR_RSA_VERIFY_FAILED );
}
md_info = mbedtls_md_info_from_type( md_alg );
if( md_info == NULL )
return( MBEDTLS_ERR_RSA_BAD_INPUT_DATA );
hashlen = mbedtls_md_get_size( md_info );
end = p + len;
/*
* Parse the ASN.1 structure inside the PKCS#1 v1.5 structure.
* Insist on 2-byte length tags, to protect against variants of
* Bleichenbacher's forgery attack against lax PKCS#1v1.5 verification.
*/
p0 = p;
if( ( ret = mbedtls_asn1_get_tag( &p, end, &asn1_len,
MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE ) ) != 0 )
return( MBEDTLS_ERR_RSA_VERIFY_FAILED );
if( p != p0 + 2 || asn1_len + 2 != len )
return( MBEDTLS_ERR_RSA_VERIFY_FAILED );
p0 = p;
if( ( ret = mbedtls_asn1_get_tag( &p, end, &asn1_len,
MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE ) ) != 0 )
return( MBEDTLS_ERR_RSA_VERIFY_FAILED );
if( p != p0 + 2 || asn1_len + 6 + hashlen != len )
return( MBEDTLS_ERR_RSA_VERIFY_FAILED );
p0 = p;
if( ( ret = mbedtls_asn1_get_tag( &p, end, &oid.len, MBEDTLS_ASN1_OID ) ) != 0 )
return( MBEDTLS_ERR_RSA_VERIFY_FAILED );
if( p != p0 + 2 )
return( MBEDTLS_ERR_RSA_VERIFY_FAILED );
oid.p = p;
p += oid.len;
if( mbedtls_oid_get_md_alg( &oid, &msg_md_alg ) != 0 )
return( MBEDTLS_ERR_RSA_VERIFY_FAILED );
if( md_alg != msg_md_alg )
return( MBEDTLS_ERR_RSA_VERIFY_FAILED );
/*
* assume the algorithm parameters must be NULL
*/
p0 = p;
if( ( ret = mbedtls_asn1_get_tag( &p, end, &asn1_len, MBEDTLS_ASN1_NULL ) ) != 0 )
return( MBEDTLS_ERR_RSA_VERIFY_FAILED );
if( p != p0 + 2 )
return( MBEDTLS_ERR_RSA_VERIFY_FAILED );
p0 = p;
if( ( ret = mbedtls_asn1_get_tag( &p, end, &asn1_len, MBEDTLS_ASN1_OCTET_STRING ) ) != 0 )
return( MBEDTLS_ERR_RSA_VERIFY_FAILED );
if( p != p0 + 2 || asn1_len != hashlen )
return( MBEDTLS_ERR_RSA_VERIFY_FAILED );
if( memcmp( p, hash, hashlen ) != 0 )
return( MBEDTLS_ERR_RSA_VERIFY_FAILED );
p += hashlen;
if( p != end )
return( MBEDTLS_ERR_RSA_VERIFY_FAILED );
return( 0 );
}
#endif /* MBEDTLS_PKCS1_V15 */