github.com/shopperooofficial/ethereum-protocol@v1.9.7/crypto/secp256k1/libsecp256k1/contrib/lax_der_parsing.h (about)

     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