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Fix pk_write with EC key to use a constant size for the private value #314

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Merged
merged 2 commits into from
Nov 8, 2019
Merged

Fix pk_write with EC key to use a constant size for the private value #314

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c212166
pk_write test cases with short/long private key
gilles-peskine-arm Aug 10, 2018
2700cfb
Fix pk_write with an EC key to write a constant-length private value
gilles-peskine-arm Aug 10, 2018
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27 changes: 24 additions & 3 deletions library/pkwrite.c
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Original file line number Diff line number Diff line change
Expand Up @@ -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"
Expand Down Expand Up @@ -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,
Expand Down Expand Up @@ -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 ) );
Expand Down
5 changes: 5 additions & 0 deletions tests/data_files/ec_256_long_prv.pem
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Original file line number Diff line number Diff line change
@@ -0,0 +1,5 @@
-----BEGIN EC PRIVATE KEY-----
MHcCAQEEIIcex4mqXsQamUKTVf8vXmTAJrQvGjh5mXG8p9+OR4xAoAoGCCqGSM49
AwEHoUQDQgAEqJ2HQjPpc6fDwE/vSa6U35USXawkTo98y4U6NsAl+rOGuqMPEFXf
P1Srm/Jrzwa/RuppRL5kgyAsGJTUmwZEzQ==
-----END EC PRIVATE KEY-----
7 changes: 7 additions & 0 deletions tests/data_files/ec_521_short_prv.pem
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Original file line number Diff line number Diff line change
@@ -0,0 +1,7 @@
-----BEGIN EC PRIVATE KEY-----
MIHcAgEBBEIAOXdk7W+Hf5L7Hc9fKe44wmpaRNs5ERFTkv5CrlXv/Bu3y28M673q
vBNo7a/UE/6NNQHu2pQODEYFpMg6R34b5SigBwYFK4EEACOhgYkDgYYABAFUMHXV
KPA4vkMgq+pFgDoH96XoM517gF2GJFV6h2gLhykzIHL/otAyEpAStw7MBvbU0V21
ixB+hjqzO7Snxaj9mwB8g87OKxm5eGfsqvJNPdJ0RZ/EKy06Ukg6KThlhQeyrtIk
g5PTCrPnNszlffAy6/jCOe3Moi59g15H13sSzwfX6g==
-----END EC PRIVATE KEY-----
8 changes: 8 additions & 0 deletions tests/suites/test_suite_pkwrite.data
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Expand Up @@ -30,10 +30,18 @@ Private key write check EC 192 bits
depends_on:MBEDTLS_ECP_C:MBEDTLS_BASE64_C:MBEDTLS_ECP_DP_SECP192R1_ENABLED
pk_write_key_check:"data_files/ec_prv.sec1.pem"

Private key write check EC 256 bits (top bit set)
depends_on:MBEDTLS_ECP_C:MBEDTLS_BASE64_C:MBEDTLS_ECP_DP_SECP256R1_ENABLED
pk_write_key_check:"data_files/ec_256_long_prv.pem"

Private key write check EC 521 bits
depends_on:MBEDTLS_ECP_C:MBEDTLS_BASE64_C:MBEDTLS_ECP_DP_SECP521R1_ENABLED
pk_write_key_check:"data_files/ec_521_prv.pem"

Private key write check EC 521 bits (top byte is 0)
depends_on:MBEDTLS_ECP_C:MBEDTLS_BASE64_C:MBEDTLS_ECP_DP_SECP521R1_ENABLED
pk_write_key_check:"data_files/ec_521_short_prv.pem"

Private key write check EC Brainpool 512 bits
depends_on:MBEDTLS_ECP_C:MBEDTLS_BASE64_C:MBEDTLS_ECP_DP_BP512R1_ENABLED
pk_write_key_check:"data_files/ec_bp512_prv.pem"