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mbedtls/library/pkwrite.c
Gilles Peskine 98add4fd5a Fix pk_write with an EC key to write a constant-length private value 
When writing a private EC key, use a constant size for the private
value, as specified in RFC 5915. Previously, the value was written
as an ASN.1 INTEGER, which caused the size of the key to leak
about 1 bit of information on average, and could cause the value to be
1 byte too large for the output buffer.
2018-09-04 11:22:08 +02:00

543 lines
17 KiB
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/*
* Public Key layer for writing key files and structures
*
* Copyright (C) 2006-2015, ARM Limited, All Rights Reserved
* SPDX-License-Identifier: Apache-2.0
*
* Licensed under the Apache License, Version 2.0 (the "License"); you may
* not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
* This file is part of mbed TLS (https://tls.mbed.org)
*/
#if !defined(MBEDTLS_CONFIG_FILE)
#include "mbedtls/config.h"
#else
#include MBEDTLS_CONFIG_FILE
#endif
#if defined(MBEDTLS_PK_WRITE_C)
#include "mbedtls/pk.h"
#include "mbedtls/asn1write.h"
#include "mbedtls/oid.h"
#include <string.h>
#if defined(MBEDTLS_RSA_C)
#include "mbedtls/rsa.h"
#endif
#if defined(MBEDTLS_ECP_C)
#include "mbedtls/bignum.h"
#include "mbedtls/ecp.h"
#endif
#if defined(MBEDTLS_ECDSA_C)
#include "mbedtls/ecdsa.h"
#endif
#if defined(MBEDTLS_PEM_WRITE_C)
#include "mbedtls/pem.h"
#endif
#if defined(MBEDTLS_PLATFORM_C)
#include "mbedtls/platform.h"
#else
#include <stdlib.h>
#define mbedtls_calloc calloc
#define mbedtls_free free
#endif
#if defined(MBEDTLS_ECP_C)
/* Implementation that should never be optimized out by the compiler */
static void mbedtls_zeroize( void *v, size_t n ) {
volatile unsigned char *p = (unsigned char*)v; while( n-- ) *p++ = 0;
}
#endif /* MBEDTLS_ECP_C */
#if defined(MBEDTLS_RSA_C)
/*
* RSAPublicKey ::= SEQUENCE {
* modulus INTEGER, -- n
* publicExponent INTEGER -- e
* }
*/
static int pk_write_rsa_pubkey( unsigned char **p, unsigned char *start,
mbedtls_rsa_context *rsa )
{
int ret;
size_t len = 0;
mbedtls_mpi T;
mbedtls_mpi_init( &T );
/* Export E */
if ( ( ret = mbedtls_rsa_export( rsa, NULL, NULL, NULL, NULL, &T ) ) != 0 ||
( ret = mbedtls_asn1_write_mpi( p, start, &T ) ) < 0 )
goto end_of_export;
len += ret;
/* Export N */
if ( ( ret = mbedtls_rsa_export( rsa, &T, NULL, NULL, NULL, NULL ) ) != 0 ||
( ret = mbedtls_asn1_write_mpi( p, start, &T ) ) < 0 )
goto end_of_export;
len += ret;
end_of_export:
mbedtls_mpi_free( &T );
if( ret < 0 )
return( ret );
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( p, start, len ) );
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( p, start, MBEDTLS_ASN1_CONSTRUCTED |
MBEDTLS_ASN1_SEQUENCE ) );
return( (int) len );
}
#endif /* MBEDTLS_RSA_C */
#if defined(MBEDTLS_ECP_C)
/*
* EC public key is an EC point
*/
static int pk_write_ec_pubkey( unsigned char **p, unsigned char *start,
mbedtls_ecp_keypair *ec )
{
int ret;
size_t len = 0;
unsigned char buf[MBEDTLS_ECP_MAX_PT_LEN];
if( ( ret = mbedtls_ecp_point_write_binary( &ec->grp, &ec->Q,
MBEDTLS_ECP_PF_UNCOMPRESSED,
&len, buf, sizeof( buf ) ) ) != 0 )
{
return( ret );
}
if( *p < start || (size_t)( *p - start ) < len )
return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );
*p -= len;
memcpy( *p, buf, len );
return( (int) len );
}
/*
* ECParameters ::= CHOICE {
* namedCurve OBJECT IDENTIFIER
* }
*/
static int pk_write_ec_param( unsigned char **p, unsigned char *start,
mbedtls_ecp_keypair *ec )
{
int ret;
size_t len = 0;
const char *oid;
size_t oid_len;
if( ( ret = mbedtls_oid_get_oid_by_ec_grp( ec->grp.id, &oid, &oid_len ) ) != 0 )
return( ret );
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_oid( p, start, oid, oid_len ) );
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_zeroize( tmp, byte_length );
return( ret );
}
#endif /* MBEDTLS_ECP_C */
int mbedtls_pk_write_pubkey( unsigned char **p, unsigned char *start,
const mbedtls_pk_context *key )
{
int ret;
size_t len = 0;
#if defined(MBEDTLS_RSA_C)
if( mbedtls_pk_get_type( key ) == MBEDTLS_PK_RSA )
MBEDTLS_ASN1_CHK_ADD( len, pk_write_rsa_pubkey( p, start, mbedtls_pk_rsa( *key ) ) );
else
#endif
#if defined(MBEDTLS_ECP_C)
if( mbedtls_pk_get_type( key ) == MBEDTLS_PK_ECKEY )
MBEDTLS_ASN1_CHK_ADD( len, pk_write_ec_pubkey( p, start, mbedtls_pk_ec( *key ) ) );
else
#endif
return( MBEDTLS_ERR_PK_FEATURE_UNAVAILABLE );
return( (int) len );
}
int mbedtls_pk_write_pubkey_der( mbedtls_pk_context *key, unsigned char *buf, size_t size )
{
int ret;
unsigned char *c;
size_t len = 0, par_len = 0, oid_len;
const char *oid;
c = buf + size;
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_pk_write_pubkey( &c, buf, key ) );
if( c - buf < 1 )
return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );
/*
* SubjectPublicKeyInfo ::= SEQUENCE {
* algorithm AlgorithmIdentifier,
* subjectPublicKey BIT STRING }
*/
*--c = 0;
len += 1;
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, buf, len ) );
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( &c, buf, MBEDTLS_ASN1_BIT_STRING ) );
if( ( ret = mbedtls_oid_get_oid_by_pk_alg( mbedtls_pk_get_type( key ),
&oid, &oid_len ) ) != 0 )
{
return( ret );
}
#if defined(MBEDTLS_ECP_C)
if( mbedtls_pk_get_type( key ) == MBEDTLS_PK_ECKEY )
{
MBEDTLS_ASN1_CHK_ADD( par_len, pk_write_ec_param( &c, buf, mbedtls_pk_ec( *key ) ) );
}
#endif
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_algorithm_identifier( &c, buf, oid, oid_len,
par_len ) );
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, buf, len ) );
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( &c, buf, MBEDTLS_ASN1_CONSTRUCTED |
MBEDTLS_ASN1_SEQUENCE ) );
return( (int) len );
}
int mbedtls_pk_write_key_der( mbedtls_pk_context *key, unsigned char *buf, size_t size )
{
int ret;
unsigned char *c = buf + size;
size_t len = 0;
#if defined(MBEDTLS_RSA_C)
if( mbedtls_pk_get_type( key ) == MBEDTLS_PK_RSA )
{
mbedtls_mpi T; /* Temporary holding the exported parameters */
mbedtls_rsa_context *rsa = mbedtls_pk_rsa( *key );
/*
* Export the parameters one after another to avoid simultaneous copies.
*/
mbedtls_mpi_init( &T );
/* Export QP */
if( ( ret = mbedtls_rsa_export_crt( rsa, NULL, NULL, &T ) ) != 0 ||
( ret = mbedtls_asn1_write_mpi( &c, buf, &T ) ) < 0 )
goto end_of_export;
len += ret;
/* Export DQ */
if( ( ret = mbedtls_rsa_export_crt( rsa, NULL, &T, NULL ) ) != 0 ||
( ret = mbedtls_asn1_write_mpi( &c, buf, &T ) ) < 0 )
goto end_of_export;
len += ret;
/* Export DP */
if( ( ret = mbedtls_rsa_export_crt( rsa, &T, NULL, NULL ) ) != 0 ||
( ret = mbedtls_asn1_write_mpi( &c, buf, &T ) ) < 0 )
goto end_of_export;
len += ret;
/* Export Q */
if ( ( ret = mbedtls_rsa_export( rsa, NULL, NULL,
&T, NULL, NULL ) ) != 0 ||
( ret = mbedtls_asn1_write_mpi( &c, buf, &T ) ) < 0 )
goto end_of_export;
len += ret;
/* Export P */
if ( ( ret = mbedtls_rsa_export( rsa, NULL, &T,
NULL, NULL, NULL ) ) != 0 ||
( ret = mbedtls_asn1_write_mpi( &c, buf, &T ) ) < 0 )
goto end_of_export;
len += ret;
/* Export D */
if ( ( ret = mbedtls_rsa_export( rsa, NULL, NULL,
NULL, &T, NULL ) ) != 0 ||
( ret = mbedtls_asn1_write_mpi( &c, buf, &T ) ) < 0 )
goto end_of_export;
len += ret;
/* Export E */
if ( ( ret = mbedtls_rsa_export( rsa, NULL, NULL,
NULL, NULL, &T ) ) != 0 ||
( ret = mbedtls_asn1_write_mpi( &c, buf, &T ) ) < 0 )
goto end_of_export;
len += ret;
/* Export N */
if ( ( ret = mbedtls_rsa_export( rsa, &T, NULL,
NULL, NULL, NULL ) ) != 0 ||
( ret = mbedtls_asn1_write_mpi( &c, buf, &T ) ) < 0 )
goto end_of_export;
len += ret;
end_of_export:
mbedtls_mpi_free( &T );
if( ret < 0 )
return( ret );
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_int( &c, buf, 0 ) );
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, buf, len ) );
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( &c,
buf, MBEDTLS_ASN1_CONSTRUCTED |
MBEDTLS_ASN1_SEQUENCE ) );
}
else
#endif /* MBEDTLS_RSA_C */
#if defined(MBEDTLS_ECP_C)
if( mbedtls_pk_get_type( key ) == MBEDTLS_PK_ECKEY )
{
mbedtls_ecp_keypair *ec = mbedtls_pk_ec( *key );
size_t pub_len = 0, par_len = 0;
/*
* RFC 5915, or SEC1 Appendix C.4
*
* ECPrivateKey ::= SEQUENCE {
* version INTEGER { ecPrivkeyVer1(1) } (ecPrivkeyVer1),
* privateKey OCTET STRING,
* parameters [0] ECParameters {{ NamedCurve }} OPTIONAL,
* publicKey [1] BIT STRING OPTIONAL
* }
*/
/* publicKey */
MBEDTLS_ASN1_CHK_ADD( pub_len, pk_write_ec_pubkey( &c, buf, ec ) );
if( c - buf < 1 )
return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );
*--c = 0;
pub_len += 1;
MBEDTLS_ASN1_CHK_ADD( pub_len, mbedtls_asn1_write_len( &c, buf, pub_len ) );
MBEDTLS_ASN1_CHK_ADD( pub_len, mbedtls_asn1_write_tag( &c, buf, MBEDTLS_ASN1_BIT_STRING ) );
MBEDTLS_ASN1_CHK_ADD( pub_len, mbedtls_asn1_write_len( &c, buf, pub_len ) );
MBEDTLS_ASN1_CHK_ADD( pub_len, mbedtls_asn1_write_tag( &c, buf,
MBEDTLS_ASN1_CONTEXT_SPECIFIC | MBEDTLS_ASN1_CONSTRUCTED | 1 ) );
len += pub_len;
/* parameters */
MBEDTLS_ASN1_CHK_ADD( par_len, pk_write_ec_param( &c, buf, ec ) );
MBEDTLS_ASN1_CHK_ADD( par_len, mbedtls_asn1_write_len( &c, buf, par_len ) );
MBEDTLS_ASN1_CHK_ADD( par_len, mbedtls_asn1_write_tag( &c, buf,
MBEDTLS_ASN1_CONTEXT_SPECIFIC | MBEDTLS_ASN1_CONSTRUCTED | 0 ) );
len += par_len;
/* 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 ) );
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_len( &c, buf, len ) );
MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_tag( &c, buf, MBEDTLS_ASN1_CONSTRUCTED |
MBEDTLS_ASN1_SEQUENCE ) );
}
else
#endif /* MBEDTLS_ECP_C */
return( MBEDTLS_ERR_PK_FEATURE_UNAVAILABLE );
return( (int) len );
}
#if defined(MBEDTLS_PEM_WRITE_C)
#define PEM_BEGIN_PUBLIC_KEY "-----BEGIN PUBLIC KEY-----\n"
#define PEM_END_PUBLIC_KEY "-----END PUBLIC KEY-----\n"
#define PEM_BEGIN_PRIVATE_KEY_RSA "-----BEGIN RSA PRIVATE KEY-----\n"
#define PEM_END_PRIVATE_KEY_RSA "-----END RSA PRIVATE KEY-----\n"
#define PEM_BEGIN_PRIVATE_KEY_EC "-----BEGIN EC PRIVATE KEY-----\n"
#define PEM_END_PRIVATE_KEY_EC "-----END EC PRIVATE KEY-----\n"
/*
* Max sizes of key per types. Shown as tag + len (+ content).
*/
#if defined(MBEDTLS_RSA_C)
/*
* RSA public keys:
* SubjectPublicKeyInfo ::= SEQUENCE { 1 + 3
* algorithm AlgorithmIdentifier, 1 + 1 (sequence)
* + 1 + 1 + 9 (rsa oid)
* + 1 + 1 (params null)
* subjectPublicKey BIT STRING } 1 + 3 + (1 + below)
* RSAPublicKey ::= SEQUENCE { 1 + 3
* modulus INTEGER, -- n 1 + 3 + MPI_MAX + 1
* publicExponent INTEGER -- e 1 + 3 + MPI_MAX + 1
* }
*/
#define RSA_PUB_DER_MAX_BYTES 38 + 2 * MBEDTLS_MPI_MAX_SIZE
/*
* RSA private keys:
* RSAPrivateKey ::= SEQUENCE { 1 + 3
* version Version, 1 + 1 + 1
* modulus INTEGER, 1 + 3 + MPI_MAX + 1
* publicExponent INTEGER, 1 + 3 + MPI_MAX + 1
* privateExponent INTEGER, 1 + 3 + MPI_MAX + 1
* prime1 INTEGER, 1 + 3 + MPI_MAX / 2 + 1
* prime2 INTEGER, 1 + 3 + MPI_MAX / 2 + 1
* exponent1 INTEGER, 1 + 3 + MPI_MAX / 2 + 1
* exponent2 INTEGER, 1 + 3 + MPI_MAX / 2 + 1
* coefficient INTEGER, 1 + 3 + MPI_MAX / 2 + 1
* otherPrimeInfos OtherPrimeInfos OPTIONAL 0 (not supported)
* }
*/
#define MPI_MAX_SIZE_2 MBEDTLS_MPI_MAX_SIZE / 2 + \
MBEDTLS_MPI_MAX_SIZE % 2
#define RSA_PRV_DER_MAX_BYTES 47 + 3 * MBEDTLS_MPI_MAX_SIZE \
+ 5 * MPI_MAX_SIZE_2
#else /* MBEDTLS_RSA_C */
#define RSA_PUB_DER_MAX_BYTES 0
#define RSA_PRV_DER_MAX_BYTES 0
#endif /* MBEDTLS_RSA_C */
#if defined(MBEDTLS_ECP_C)
/*
* EC public keys:
* SubjectPublicKeyInfo ::= SEQUENCE { 1 + 2
* algorithm AlgorithmIdentifier, 1 + 1 (sequence)
* + 1 + 1 + 7 (ec oid)
* + 1 + 1 + 9 (namedCurve oid)
* subjectPublicKey BIT STRING 1 + 2 + 1 [1]
* + 1 (point format) [1]
* + 2 * ECP_MAX (coords) [1]
* }
*/
#define ECP_PUB_DER_MAX_BYTES 30 + 2 * MBEDTLS_ECP_MAX_BYTES
/*
* EC private keys:
* ECPrivateKey ::= SEQUENCE { 1 + 2
* version INTEGER , 1 + 1 + 1
* privateKey OCTET STRING, 1 + 1 + ECP_MAX
* parameters [0] ECParameters OPTIONAL, 1 + 1 + (1 + 1 + 9)
* publicKey [1] BIT STRING OPTIONAL 1 + 2 + [1] above
* }
*/
#define ECP_PRV_DER_MAX_BYTES 29 + 3 * MBEDTLS_ECP_MAX_BYTES
#else /* MBEDTLS_ECP_C */
#define ECP_PUB_DER_MAX_BYTES 0
#define ECP_PRV_DER_MAX_BYTES 0
#endif /* MBEDTLS_ECP_C */
#define PUB_DER_MAX_BYTES RSA_PUB_DER_MAX_BYTES > ECP_PUB_DER_MAX_BYTES ? \
RSA_PUB_DER_MAX_BYTES : ECP_PUB_DER_MAX_BYTES
#define PRV_DER_MAX_BYTES RSA_PRV_DER_MAX_BYTES > ECP_PRV_DER_MAX_BYTES ? \
RSA_PRV_DER_MAX_BYTES : ECP_PRV_DER_MAX_BYTES
int mbedtls_pk_write_pubkey_pem( mbedtls_pk_context *key, unsigned char *buf, size_t size )
{
int ret;
unsigned char output_buf[PUB_DER_MAX_BYTES];
size_t olen = 0;
if( ( ret = mbedtls_pk_write_pubkey_der( key, output_buf,
sizeof(output_buf) ) ) < 0 )
{
return( ret );
}
if( ( ret = mbedtls_pem_write_buffer( PEM_BEGIN_PUBLIC_KEY, PEM_END_PUBLIC_KEY,
output_buf + sizeof(output_buf) - ret,
ret, buf, size, &olen ) ) != 0 )
{
return( ret );
}
return( 0 );
}
int mbedtls_pk_write_key_pem( mbedtls_pk_context *key, unsigned char *buf, size_t size )
{
int ret;
unsigned char output_buf[PRV_DER_MAX_BYTES];
const char *begin, *end;
size_t olen = 0;
if( ( ret = mbedtls_pk_write_key_der( key, output_buf, sizeof(output_buf) ) ) < 0 )
return( ret );
#if defined(MBEDTLS_RSA_C)
if( mbedtls_pk_get_type( key ) == MBEDTLS_PK_RSA )
{
begin = PEM_BEGIN_PRIVATE_KEY_RSA;
end = PEM_END_PRIVATE_KEY_RSA;
}
else
#endif
#if defined(MBEDTLS_ECP_C)
if( mbedtls_pk_get_type( key ) == MBEDTLS_PK_ECKEY )
{
begin = PEM_BEGIN_PRIVATE_KEY_EC;
end = PEM_END_PRIVATE_KEY_EC;
}
else
#endif
return( MBEDTLS_ERR_PK_FEATURE_UNAVAILABLE );
if( ( ret = mbedtls_pem_write_buffer( begin, end,
output_buf + sizeof(output_buf) - ret,
ret, buf, size, &olen ) ) != 0 )
{
return( ret );
}
return( 0 );
}
#endif /* MBEDTLS_PEM_WRITE_C */
#endif /* MBEDTLS_PK_WRITE_C */
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