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Merge pull request #314 from gilles-peskine-arm/pkwrite_ECPrivateKey_size-crypto

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Fix pk_write with EC key to use a constant size for the private value
This commit is contained in:
Gilles Peskine 2019-11-08 19:30:51 +01:00 • committed by GitHub
commit 2ad5e45de6
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GPG key ID: 4AEE18F83AFDEB23
4 changed files with 44 additions and 3 deletions
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27
library/pkwrite.c
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@ -38,7 +38,9 @@
#include "mbedtls/rsa.h"
#endif
#if defined(MBEDTLS_ECP_C)
#include "mbedtls/bignum.h"
#include "mbedtls/ecp.h"
#include "mbedtls/platform_util.h"
#endif
#if defined(MBEDTLS_ECDSA_C)
#include "mbedtls/ecdsa.h"
@ -154,6 +156,26 @@ static int pk_write_ec_param( unsigned char **p, unsigned char *start,
return( (int) len );
}
/*
* privateKey OCTET STRING -- always of length ceil(log2(n)/8)
*/
static int pk_write_ec_private( unsigned char **p, unsigned char *start,
mbedtls_ecp_keypair *ec )
{
int ret;
size_t byte_length = ( ec->grp.pbits + 7 ) / 8;
unsigned char tmp[MBEDTLS_ECP_MAX_BYTES];
ret = mbedtls_mpi_write_binary( &ec->d, tmp, byte_length );
if( ret != 0 )
goto exit;
ret = mbedtls_asn1_write_octet_string( p, start, tmp, byte_length );
exit:
mbedtls_platform_zeroize( tmp, byte_length );
return( ret );
}
#endif /* MBEDTLS_ECP_C */
int mbedtls_pk_write_pubkey( unsigned char **p, unsigned char *start,
@ -424,9 +446,8 @@ int mbedtls_pk_write_key_der( mbedtls_pk_context *key, unsigned char *buf, size_
MBEDTLS_ASN1_CONTEXT_SPECIFIC | MBEDTLS_ASN1_CONSTRUCTED | 0 ) );
len += par_len;
/* privateKey: write as MPI then fix tag */
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_mpi( &c, buf, &ec->d ) );
*c = MBEDTLS_ASN1_OCTET_STRING;
/* privateKey */
MBEDTLS_ASN1_CHK_ADD( len, pk_write_ec_private( &c, buf, ec ) );
/* version */
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_int( &c, buf, 1 ) );