src/secp256k1/contrib/lax_der_parsing.h

   1 /**********************************************************************
   2  * Copyright (c) 2015 Pieter Wuille                                   *
   3  * Distributed under the MIT software license, see the accompanying   *
   4  * file COPYING or http://www.opensource.org/licenses/mit-license.php.*
   5  **********************************************************************/
   6
   7 /****
   8  * Please do not link this file directly. It is not part of the libsecp256k1
   9  * project and does not promise any stability in its API, functionality or
  10  * presence. Projects which use this code should instead copy this header
  11  * and its accompanying .c file directly into their codebase.
  12  ****/
  13
  14 /* This file defines a function that parses DER with various errors and
  15  * violations. This is not a part of the library itself, because the allowed
  16  * violations are chosen arbitrarily and do not follow or establish any
  17  * standard.
  18  *
  19  * In many places it matters that different implementations do not only accept
  20  * the same set of valid signatures, but also reject the same set of signatures.
  21  * The only means to accomplish that is by strictly obeying a standard, and not
  22  * accepting anything else.
  23  *
  24  * Nonetheless, sometimes there is a need for compatibility with systems that
  25  * use signatures which do not strictly obey DER. The snippet below shows how
  26  * certain violations are easily supported. You may need to adapt it.
  27  *
  28  * Do not use this for new systems. Use well-defined DER or compact signatures
  29  * instead if you have the choice (see secp256k1_ecdsa_signature_parse_der and
  30  * secp256k1_ecdsa_signature_parse_compact).
  31  *
  32  * The supported violations are:
  33  * - All numbers are parsed as nonnegative integers, even though X.609-0207
  34  *   section 8.3.3 specifies that integers are always encoded as two's
  35  *   complement.
  36  * - Integers can have length 0, even though section 8.3.1 says they can't.
  37  * - Integers with overly long padding are accepted, violation section
  38  *   8.3.2.
  39  * - 127-byte long length descriptors are accepted, even though section
  40  *   8.1.3.5.c says that they are not.
  41  * - Trailing garbage data inside or after the signature is ignored.
  42  * - The length descriptor of the sequence is ignored.
  43  *
  44  * Compared to for example OpenSSL, many violations are NOT supported:
  45  * - Using overly long tag descriptors for the sequence or integers inside,
  46  *   violating section 8.1.2.2.
  47  * - Encoding primitive integers as constructed values, violating section
  48  *   8.3.1.
  49  */
  50
  51 #ifndef _SECP256K1_CONTRIB_LAX_DER_PARSING_H_
  52 #define _SECP256K1_CONTRIB_LAX_DER_PARSING_H_
  53
  54 #include <secp256k1.h>
  55
  56 # ifdef __cplusplus
  57 extern "C" {
  58 # endif
  59
  60 /** Parse a signature in "lax DER" format
  61  *
  62  *  Returns: 1 when the signature could be parsed, 0 otherwise.
  63  *  Args: ctx:      a secp256k1 context object
  64  *  Out:  sig:      a pointer to a signature object
  65  *  In:   input:    a pointer to the signature to be parsed
  66  *        inputlen: the length of the array pointed to be input
  67  *
  68  *  This function will accept any valid DER encoded signature, even if the
  69  *  encoded numbers are out of range. In addition, it will accept signatures
  70  *  which violate the DER spec in various ways. Its purpose is to allow
  71  *  validation of the Bitcoin blockchain, which includes non-DER signatures
  72  *  from before the network rules were updated to enforce DER. Note that
  73  *  the set of supported violations is a strict subset of what OpenSSL will
  74  *  accept.
  75  *
  76  *  After the call, sig will always be initialized. If parsing failed or the
  77  *  encoded numbers are out of range, signature validation with it is
  78  *  guaranteed to fail for every message and public key.
  79  */
  80 int ecdsa_signature_parse_der_lax(
  81     const secp256k1_context* ctx,
  82     secp256k1_ecdsa_signature* sig,
  83     const unsigned char *input,
  84     size_t inputlen
  85 ) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);
  86
  87 #ifdef __cplusplus
  88 }
  89 #endif
  90
  91 #endif