diff options
Diffstat (limited to 'src/secp256k1/contrib/lax_der_parsing.h')
-rw-r--r-- | src/secp256k1/contrib/lax_der_parsing.h | 91 |
1 files changed, 91 insertions, 0 deletions
diff --git a/src/secp256k1/contrib/lax_der_parsing.h b/src/secp256k1/contrib/lax_der_parsing.h new file mode 100644 index 0000000000..7eaf63bf6a --- /dev/null +++ b/src/secp256k1/contrib/lax_der_parsing.h @@ -0,0 +1,91 @@ +/********************************************************************** + * 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 + +/** 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 */ |