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/*
* Copyright 2019 The OpenSSL Project Authors. All Rights Reserved.
*
* Licensed under the Apache License 2.0 (the "License"). You may not use
* this file except in compliance with the License. You can obtain a copy
* in the file LICENSE in the source distribution or at
* https://www.openssl.org/source/license.html
*/
/*
* A simple ASN.1 DER encoder/decoder for DSA-Sig-Value and ECDSA-Sig-Value.
*
* DSA-Sig-Value ::= SEQUENCE {
* r INTEGER,
* s INTEGER
* }
*
* ECDSA-Sig-Value ::= SEQUENCE {
* r INTEGER,
* s INTEGER
* }
*/
#include <openssl/crypto.h>
#include <openssl/bn.h>
#include "internal/asn1_dsa.h"
#define ID_SEQUENCE 0x30
#define ID_INTEGER 0x02
/*
* Outputs the encoding of the length octets for a DER value with a content
* length of cont_len bytes to *ppout and, if successful, increments *ppout
* past the data just written.
*
* The maximum supported content length is 65535 (0xffff) bytes.
* The maximum returned length in bytes of the encoded output is 3.
*
* If ppout is NULL then the output size is calculated and returned but no
* output is produced.
* If ppout is not NULL then *ppout must not be NULL.
*
* An attempt to produce more than len bytes results in an error.
* Returns the number of bytes of output produced (or that would be produced)
* or 0 if an error occurs.
*/
size_t encode_der_length(size_t cont_len, unsigned char **ppout, size_t len)
{
size_t encoded_len;
if (cont_len <= 0x7f) {
encoded_len = 1;
} else if (cont_len <= 0xff) {
encoded_len = 2;
} else if (cont_len <= 0xffff) {
encoded_len = 3;
} else {
/* Too large for supported length encodings */
return 0;
}
if (encoded_len > len)
return 0;
if (ppout != NULL) {
unsigned char *out = *ppout;
switch (encoded_len) {
case 2:
*out++ = 0x81;
break;
case 3:
*out++ = 0x82;
*out++ = (unsigned char)(cont_len >> 8);
break;
}
*out++ = (unsigned char)cont_len;
*ppout = out;
}
return encoded_len;
}
/*
* Outputs the DER encoding of a positive ASN.1 INTEGER to *ppout and, if
* successful, increments *ppout past the data just written.
*
* If n is negative then an error results.
* If ppout is NULL then the output size is calculated and returned but no
* output is produced.
* If ppout is not NULL then *ppout must not be NULL.
*
* An attempt to produce more than len bytes results in an error.
* Returns the number of bytes of output produced (or that would be produced)
* or 0 if an error occurs.
*/
size_t encode_der_integer(const BIGNUM *n, unsigned char **ppout, size_t len)
{
unsigned char *out = NULL;
unsigned char **pp = NULL;
size_t produced;
size_t c;
size_t cont_len;
if (len < 1 || BN_is_negative(n))
return 0;
/*
* Calculate the ASN.1 INTEGER DER content length for n.
* This is the number of whole bytes required to represent n (i.e. rounded
* down), plus one.
* If n is zero then the content is a single zero byte (length = 1).
* If the number of bits of n is a multiple of 8 then an extra zero padding
* byte is included to ensure that the value is still treated as positive
* in the INTEGER two's complement representation.
*/
cont_len = BN_num_bits(n) / 8 + 1;
if (ppout != NULL) {
out = *ppout;
pp = &out;
*out++ = ID_INTEGER;
}
produced = 1;
if ((c = encode_der_length(cont_len, pp, len - produced)) == 0)
return 0;
produced += c;
if (cont_len > len - produced)
return 0;
if (pp != NULL) {
if (BN_bn2binpad(n, out, (int)cont_len) != (int)cont_len)
return 0;
out += cont_len;
*ppout = out;
}
produced += cont_len;
return produced;
}
/*
* Outputs the DER encoding of a DSA-Sig-Value or ECDSA-Sig-Value to *ppout
* and increments *ppout past the data just written.
*
* If ppout is NULL then the output size is calculated and returned but no
* output is produced.
* If ppout is not NULL then *ppout must not be NULL.
*
* An attempt to produce more than len bytes results in an error.
* Returns the number of bytes of output produced (or that would be produced)
* or 0 if an error occurs.
*/
size_t encode_der_dsa_sig(const BIGNUM *r, const BIGNUM *s,
unsigned char **ppout, size_t len)
{
unsigned char *out = NULL;
unsigned char **pp = NULL;
size_t produced;
size_t c;
size_t r_der_len;
size_t s_der_len;
size_t cont_len;
if (len < 1
|| (r_der_len = encode_der_integer(r, NULL, SIZE_MAX)) == 0
|| (s_der_len = encode_der_integer(s, NULL, SIZE_MAX)) == 0)
return 0;
cont_len = r_der_len + s_der_len;
if (ppout != NULL) {
out = *ppout;
pp = &out;
*out++ = ID_SEQUENCE;
}
produced = 1;
if ((c = encode_der_length(cont_len, pp, len - produced)) == 0)
return 0;
produced += c;
if ((c = encode_der_integer(r, pp, len - produced)) == 0)
return 0;
produced += c;
if ((c = encode_der_integer(s, pp, len - produced)) == 0)
return 0;
produced += c;
if (pp != NULL)
*ppout = out;
return produced;
}
/*
* Decodes the DER length octets at *ppin, stores the decoded length to
* *pcont_len and, if successful, increments *ppin past the data that was
* consumed.
*
* pcont_len, ppin and *ppin must not be NULL.
*
* An attempt to consume more than len bytes results in an error.
* Returns the number of bytes of input consumed or 0 if an error occurs.
*/
size_t decode_der_length(size_t *pcont_len, const unsigned char **ppin,
size_t len)
{
const unsigned char *in = *ppin;
size_t consumed;
size_t n;
if (len < 1)
return 0;
n = *in++;
consumed = 1;
if (n > 0x7f) {
if (n == 0x81 && len - consumed >= 1) {
n = *in++;
if (n <= 0x7f)
return 0; /* Not DER. */
++consumed;
} else if (n == 0x82 && len - consumed >= 2) {
n = *in++ << 8;
n |= *in++;
if (n <= 0xff)
return 0; /* Not DER. */
consumed += 2;
} else {
return 0; /* Too large, invalid, or not DER. */
}
}
*pcont_len = n;
*ppin = in;
return consumed;
}
/*
* Decodes a single ASN.1 INTEGER value from *ppin, which must be DER encoded,
* updates n with the decoded value, and, if successful, increments *ppin past
* the data that was consumed.
*
* The BIGNUM, n, must have already been allocated by calling BN_new().
* ppin and *ppin must not be NULL.
*
* An attempt to consume more than len bytes results in an error.
* Returns the number of bytes of input consumed or 0 if an error occurs.
*
* If the buffer is supposed to only contain a single INTEGER value with no
* trailing garbage then it is up to the caller to verify that all bytes
* were consumed.
*/
size_t decode_der_integer(BIGNUM *n, const unsigned char **ppin, size_t len)
{
const unsigned char *in = *ppin;
size_t consumed;
size_t c;
size_t cont_len;
if (len < 1 || n == NULL || *in++ != ID_INTEGER)
return 0;
consumed = 1;
if ((c = decode_der_length(&cont_len, &in, len - consumed)) == 0)
return 0;
consumed += c;
/* Check for a positive INTEGER with valid content encoding and decode. */
if (cont_len > len - consumed || cont_len < 1 || (in[0] & 0x80) != 0
|| (cont_len >= 2 && in[0] == 0 && (in[1] & 0x80) == 0)
|| BN_bin2bn(in, (int)cont_len, n) == NULL)
return 0;
in += cont_len;
consumed += cont_len;
*ppin = in;
return consumed;
}
static size_t decode_dsa_sig_content(BIGNUM *r, BIGNUM *s,
const unsigned char **ppin, size_t len)
{
const unsigned char *in = *ppin;
size_t consumed = 0;
size_t
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