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92 lines
3.9 KiB
C
92 lines
3.9 KiB
C
/**********************************************************************
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* Copyright (c) 2015 Pieter Wuille *
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* Distributed under the MIT software license, see the accompanying *
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* file COPYING or http://www.opensource.org/licenses/mit-license.php.*
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**********************************************************************/
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/****
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* Please do not link this file directly. It is not part of the libsecp256k1
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* project and does not promise any stability in its API, functionality or
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* presence. Projects which use this code should instead copy this header
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* and its accompanying .c file directly into their codebase.
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****/
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/* This file defines a function that parses DER with various errors and
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* violations. This is not a part of the library itself, because the allowed
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* violations are chosen arbitrarily and do not follow or establish any
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* standard.
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*
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* In many places it matters that different implementations do not only accept
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* the same set of valid signatures, but also reject the same set of signatures.
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* The only means to accomplish that is by strictly obeying a standard, and not
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* accepting anything else.
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*
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* Nonetheless, sometimes there is a need for compatibility with systems that
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* use signatures which do not strictly obey DER. The snippet below shows how
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* certain violations are easily supported. You may need to adapt it.
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*
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* Do not use this for new systems. Use well-defined DER or compact signatures
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* instead if you have the choice (see secp256k1_ecdsa_signature_parse_der and
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* secp256k1_ecdsa_signature_parse_compact).
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*
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* The supported violations are:
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* - All numbers are parsed as nonnegative integers, even though X.609-0207
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* section 8.3.3 specifies that integers are always encoded as two's
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* complement.
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* - Integers can have length 0, even though section 8.3.1 says they can't.
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* - Integers with overly long padding are accepted, violation section
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* 8.3.2.
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* - 127-byte long length descriptors are accepted, even though section
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* 8.1.3.5.c says that they are not.
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* - Trailing garbage data inside or after the signature is ignored.
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* - The length descriptor of the sequence is ignored.
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*
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* Compared to for example OpenSSL, many violations are NOT supported:
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* - Using overly long tag descriptors for the sequence or integers inside,
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* violating section 8.1.2.2.
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* - Encoding primitive integers as constructed values, violating section
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* 8.3.1.
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*/
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#ifndef SECP256K1_CONTRIB_LAX_DER_PARSING_H
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#define SECP256K1_CONTRIB_LAX_DER_PARSING_H
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#include <secp256k1.h>
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#ifdef __cplusplus
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extern "C" {
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#endif
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/** Parse a signature in "lax DER" format
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*
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* Returns: 1 when the signature could be parsed, 0 otherwise.
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* Args: ctx: a secp256k1 context object
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* Out: sig: a pointer to a signature object
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* In: input: a pointer to the signature to be parsed
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* inputlen: the length of the array pointed to be input
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*
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* This function will accept any valid DER encoded signature, even if the
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* encoded numbers are out of range. In addition, it will accept signatures
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* which violate the DER spec in various ways. Its purpose is to allow
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* validation of the Bitcoin blockchain, which includes non-DER signatures
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* from before the network rules were updated to enforce DER. Note that
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* the set of supported violations is a strict subset of what OpenSSL will
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* accept.
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*
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* After the call, sig will always be initialized. If parsing failed or the
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* encoded numbers are out of range, signature validation with it is
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* guaranteed to fail for every message and public key.
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*/
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int ecdsa_signature_parse_der_lax(
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const secp256k1_context* ctx,
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secp256k1_ecdsa_signature* sig,
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const unsigned char *input,
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size_t inputlen
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) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);
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#ifdef __cplusplus
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}
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#endif
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#endif /* SECP256K1_CONTRIB_LAX_DER_PARSING_H */
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