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pk_wrap: rework signature extraction to work with small r and s values

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There is a probability that r will be encoded as 31 or less bytes in DER,
so additional padding is added in such case.
Added a signature-part extraction function to tidy up the code further.
This commit is contained in:
Andrzej Kurek 2018-11-19 17:01:16 -05:00
parent 2baae9ef71
commit b7b0478f76
1 changed files with 66 additions and 42 deletions
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108
library/pk_wrap.c
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@ -479,70 +479,93 @@ static int ecdsa_can_do( mbedtls_pk_type_t type )
}
#if defined(MBEDTLS_USE_PSA_CRYPTO)
/*
* Extract one signature part of an ASN.1 integer type to a given buffer
* and adjust padding according to part_size.
*/
static int extract_ecdsa_sig_part( unsigned char **from, const unsigned char *end,
unsigned char *to, size_t part_size )
{
int ret;
size_t len_total, len_partial, zero_padding;
if( ( ret = mbedtls_asn1_get_tag( from, end, &len_partial,
MBEDTLS_ASN1_INTEGER ) ) != 0 )
{
return( ret );
}
while( **from == '\0' && len_partial > 0 )
{
( *from )++;
len_partial--;
}
if( len_partial > part_size || len_partial == 0 )
return( MBEDTLS_ERR_PK_SIG_LEN_MISMATCH );
zero_padding = part_size - len_partial;
memcpy( to + zero_padding, *from, len_partial );
len_total = len_partial + zero_padding;
while( zero_padding > 0 )
{
zero_padding--;
to[zero_padding] = 0;
}
( *from ) += len_partial;
return len_total;
}
/*
* Convert a signature from an ASN.1 sequence of two integers
* to a raw {r,s} buffer. Note: upon a successful call, the caller
* takes ownership of the sig->p buffer.
*/
static int extract_ecdsa_sig( unsigned char **p, const unsigned char *end,
mbedtls_asn1_buf *sig )
mbedtls_asn1_buf *sig, size_t int_size )
{
int ret, tag_type;
size_t len_signature, len_partial;
int ret;
if( ( end - *p ) < 1 )
{
return( MBEDTLS_ERR_ASN1_OUT_OF_DATA );
}
tag_type = **p;
if( ( ret = mbedtls_asn1_get_tag( p, end, &len_partial,
MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE ) ) != 0 )
{
return( ret );
}
if( ( ret = mbedtls_asn1_get_tag( p, end, &len_partial, MBEDTLS_ASN1_INTEGER ) )
!= 0 )
return( ret );
if( **p == '\0' )
{
( *p )++;
len_partial--;
}
sig->p = mbedtls_calloc( 2, len_partial );
sig->p = mbedtls_calloc( 2, int_size );
if( sig->p == NULL )
return( MBEDTLS_ERR_ASN1_ALLOC_FAILED );
memcpy( sig->p, *p, len_partial );
len_signature = len_partial;
( *p ) += len_partial;
if( ( ret = mbedtls_asn1_get_tag( p, end, &len_partial,
MBEDTLS_ASN1_INTEGER ) ) != 0 )
sig->tag = **p;
if( ( ret = mbedtls_asn1_get_tag( p, end, &sig->len,
MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE ) ) != 0 )
{
mbedtls_free( sig->p );
sig->p = NULL;
return( ret );
goto cleanup;
}
if( **p == '\0' )
/* Extract r */
if( ( ret = extract_ecdsa_sig_part( p, end, sig->p, int_size ) ) < 0)
{
( *p )++;
len_partial--;
goto cleanup;
}
sig->len = ret;
// Check if both parts are of the same size
if( len_partial != len_signature )
return( MBEDTLS_ERR_PK_SIG_LEN_MISMATCH );
/* Extract s */
if( ( ret = extract_ecdsa_sig_part( p, end, sig->p + sig->len, int_size ) ) < 0)
{
goto cleanup;
}
sig->len += ret;
memcpy( sig->p + len_partial, *p, len_partial );
len_signature += len_partial;
sig->tag = tag_type;
sig->len = len_signature;
( *p ) += len_partial;
return( 0 );
cleanup:
mbedtls_free( sig->p );
sig->p = NULL;
sig->len = 0;
sig->tag = 0;
return( ret );
}
static psa_ecc_curve_t mbedtls_ecc_group_to_psa( mbedtls_ecp_group_id grpid )
@ -637,7 +660,8 @@ static int ecdsa_verify_wrap( void *ctx, mbedtls_md_type_t md_alg,
psa_type = PSA_KEY_TYPE_ECC_PUBLIC_KEY( curve );
if( ( ret = extract_ecdsa_sig( &p, p + sig_len, &signature ) ) != 0 )
if( ( ret = extract_ecdsa_sig( &p, p + sig_len, &signature,
( ( (mbedtls_ecdsa_context *) ctx )->grp.nbits + 7) / 8 ) ) != 0 )
return( ret );
key_len = mbedtls_pk_write_pubkey_der( &key, buf, buf_len );
@ -678,7 +702,7 @@ static int ecdsa_verify_wrap( void *ctx, mbedtls_md_type_t md_alg,
}
ret = 0;
cleanup:
cleanup:
psa_destroy_key( key_slot );
mbedtls_free( signature.p );
return( ret );