lax_der_parsing.h

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/**********************************************************************
 * Copyright (c) 2015 Pieter Wuille                                   *
 * Distributed under the MIT software license, see the accompanying   *
 * file COPYING or http://www.opensource.org/licenses/mit-license.php.*
 **********************************************************************/

/****
 * Please do not link this file directly. It is not part of the libsecp256k1
 * project and does not promise any stability in its API, functionality or
 * presence. Projects which use this code should instead copy this header
 * and its accompanying .c file directly into their codebase.
 ****/

/* This file defines a function that parses DER with various errors and
 * violations. This is not a part of the library itself, because the allowed
 * violations are chosen arbitrarily and do not follow or establish any
 * standard.
 *
 * In many places it matters that different implementations do not only accept
 * the same set of valid signatures, but also reject the same set of signatures.
 * The only means to accomplish that is by strictly obeying a standard, and not
 * accepting anything else.
 *
 * Nonetheless, sometimes there is a need for compatibility with systems that
 * use signatures which do not strictly obey DER. The snippet below shows how
 * certain violations are easily supported. You may need to adapt it.
 *
 * Do not use this for new systems. Use well-defined DER or compact signatures
 * instead if you have the choice (see secp256k1_ecdsa_signature_parse_der and
 * secp256k1_ecdsa_signature_parse_compact).
 *
 * The supported violations are:
 * - All numbers are parsed as nonnegative integers, even though X.609-0207
 *   section 8.3.3 specifies that integers are always encoded as two's
 *   complement.
 * - Integers can have length 0, even though section 8.3.1 says they can't.
 * - Integers with overly long padding are accepted, violation section
 *   8.3.2.
 * - 127-byte long length descriptors are accepted, even though section
 *   8.1.3.5.c says that they are not.
 * - Trailing garbage data inside or after the signature is ignored.
 * - The length descriptor of the sequence is ignored.
 *
 * Compared to for example OpenSSL, many violations are NOT supported:
 * - Using overly long tag descriptors for the sequence or integers inside,
 *   violating section 8.1.2.2.
 * - Encoding primitive integers as constructed values, violating section
 *   8.3.1.
 */

#ifndef SECP256K1_CONTRIB_LAX_DER_PARSING_H
#define SECP256K1_CONTRIB_LAX_DER_PARSING_H

#include <secp256k1.h>

#ifdef __cplusplus
extern "C" {
#endif

int ecdsa_signature_parse_der_lax(
    const secp256k1_context* ctx,
    secp256k1_ecdsa_signature* sig,
    const unsigned char *input,
    size_t inputlen
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);

#ifdef __cplusplus
}
#endif

#endif /* SECP256K1_CONTRIB_LAX_DER_PARSING_H */