/********************************************************************** * 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 #ifdef __cplusplus extern "C" { #endif /** Parse a signature in "lax DER" format * * Returns: 1 when the signature could be parsed, 0 otherwise. * Args: ctx: a secp256k1 context object * Out: sig: a pointer to a signature object * In: input: a pointer to the signature to be parsed * inputlen: the length of the array pointed to be input * * This function will accept any valid DER encoded signature, even if the * encoded numbers are out of range. In addition, it will accept signatures * which violate the DER spec in various ways. Its purpose is to allow * validation of the Bitcoin blockchain, which includes non-DER signatures * from before the network rules were updated to enforce DER. Note that * the set of supported violations is a strict subset of what OpenSSL will * accept. * * After the call, sig will always be initialized. If parsing failed or the * encoded numbers are out of range, signature validation with it is * guaranteed to fail for every message and public key. */ 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 */