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Use in-place decryption in pk_parse_pkcs8_encrypted_der

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The stack buffer used to hold the decrypted key in pk_parse_pkcs8_encrypted_der
was statically sized to 2048 bytes, which is not enough for DER encoded 4096bit
RSA keys.

This commit resolves the problem by performing the key-decryption in-place,
circumventing the introduction of another stack or heap copy of the key.

There are two situations where pk_parse_pkcs8_encrypted_der is invoked:
1. When processing a PEM-encoded encrypted key in pk_parse_key.
   This does not need adaption since the PEM context used to hold the decoded
   key is already constructed and owned by pk_parse_key.
2. When processing a DER-encoded encrypted key in pk_parse_key.
   In this case, pk_parse_key calls pk_parse_pkcs8_encrypted_der with
   the buffer provided by the user, which is declared const. The commit
   therefore adds a small code paths making a copy of the keybuffer before
   calling pk_parse_pkcs8_encrypted_der.
This commit is contained in:
Hanno Becker 2017-09-28 16:46:24 +01:00
parent a75a459143
commit 713c9e187f
1 changed files with 22 additions and 13 deletions
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27
library/pkparse.c
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@ -930,12 +930,12 @@ static int pk_parse_key_pkcs8_unencrypted_der(
#if defined(POLARSSL_PKCS12_C) || defined(POLARSSL_PKCS5_C) #if defined(POLARSSL_PKCS12_C) || defined(POLARSSL_PKCS5_C)
static int pk_parse_key_pkcs8_encrypted_der( static int pk_parse_key_pkcs8_encrypted_der(
pk_context *pk, pk_context *pk,
const unsigned char *key, size_t keylen, unsigned char *key, size_t keylen,
const unsigned char *pwd, size_t pwdlen ) const unsigned char *pwd, size_t pwdlen )
{ {
int ret, decrypted = 0; int ret, decrypted = 0;
size_t len; size_t len;
unsigned char buf[2048]; unsigned char *buf;
unsigned char *p, *end; unsigned char *p, *end;
asn1_buf pbe_alg_oid, pbe_params; asn1_buf pbe_alg_oid, pbe_params;
#if defined(POLARSSL_PKCS12_C) #if defined(POLARSSL_PKCS12_C)
@ -943,8 +943,6 @@ static int pk_parse_key_pkcs8_encrypted_der(
md_type_t md_alg; md_type_t md_alg;
#endif #endif
memset( buf, 0, sizeof( buf ) );
p = (unsigned char *) key; p = (unsigned char *) key;
end = p + keylen; end = p + keylen;
@ -979,8 +977,7 @@ static int pk_parse_key_pkcs8_encrypted_der(
if( ( ret = asn1_get_tag( &p, end, &len, ASN1_OCTET_STRING ) ) != 0 ) if( ( ret = asn1_get_tag( &p, end, &len, ASN1_OCTET_STRING ) ) != 0 )
return( POLARSSL_ERR_PK_KEY_INVALID_FORMAT + ret ); return( POLARSSL_ERR_PK_KEY_INVALID_FORMAT + ret );
if( len > sizeof( buf ) ) buf = p;
return( POLARSSL_ERR_PK_BAD_INPUT_DATA );
/* /*
* Decrypt EncryptedData with appropriate PDE * Decrypt EncryptedData with appropriate PDE
@ -1170,12 +1167,24 @@ int pk_parse_key( pk_context *pk,
* error * error
*/ */
#if defined(POLARSSL_PKCS12_C) || defined(POLARSSL_PKCS5_C) #if defined(POLARSSL_PKCS12_C) || defined(POLARSSL_PKCS5_C)
if( ( ret = pk_parse_key_pkcs8_encrypted_der( pk, key, keylen,
pwd, pwdlen ) ) == 0 )
{ {
return( 0 ); unsigned char *key_copy;
if( ( key_copy = polarssl_malloc( keylen ) ) == NULL )
return( POLARSSL_ERR_PK_MALLOC_FAILED );
memcpy( key_copy, key, keylen );
ret = pk_parse_key_pkcs8_encrypted_der( pk, key_copy, keylen,
pwd, pwdlen );
polarssl_zeroize( key_copy, keylen );
polarssl_free( key_copy );
} }
if( ret == 0 )
return( 0 );
pk_free( pk ); pk_free( pk );
if( ret == POLARSSL_ERR_PK_PASSWORD_MISMATCH ) if( ret == POLARSSL_ERR_PK_PASSWORD_MISMATCH )