bitcoin/contrib/lax_der_privatekey_parsing.h

/**********************************************************************
 * Copyright (c) 2014, 2015 Pieter Wuille                             *
 * Distributed under the MIT software license, see the accompanying   *
 * file COPYING or http://www.opensource.org/licenses/mit-license.php.*
 **********************************************************************/

/* This file contains code snippets that parse DER private keys 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.
 *
 * It also contains code to serialize private keys in a compatible
 * manner.
 *
 * These functions are meant for compatibility with applications
 * that require BER encoded keys. When working with secp256k1-specific
 * code, the simple 32-byte private keys normally used by the
 * library are sufficient.
 */

#ifndef _SECP256K1_CONTRIB_BER_PRIVATEKEY_H_
#define _SECP256K1_CONTRIB_BER_PRIVATEKEY_H_

#include <string.h>
#include <secp256k1.h>

/** Export a private key in DER format.
 *
 *  Returns: 1 if the private key was valid.
 *  Args: ctx:        pointer to a context object, initialized for signing (cannot
 *                    be NULL)
 *  Out: privkey:     pointer to an array for storing the private key in BER.
 *                    Should have space for 279 bytes, and cannot be NULL.
 *       privkeylen:  Pointer to an int where the length of the private key in
 *                    privkey will be stored.
 *  In:  seckey:      pointer to a 32-byte secret key to export.
 *       compressed:  1 if the key should be exported in
 *                    compressed format, 0 otherwise
 *
 *  This function is purely meant for compatibility with applications that
 *  require BER encoded keys. When working with secp256k1-specific code, the
 *  simple 32-byte private keys are sufficient.
 *
 *  Note that this function does not guarantee correct DER output. It is
 *  guaranteed to be parsable by secp256k1_ec_privkey_import_der
 */
static SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_privkey_export_der(
    const secp256k1_context* ctx,
    unsigned char *privkey,
    size_t *privkeylen,
    const unsigned char *seckey,
    int compressed
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3) SECP256K1_ARG_NONNULL(4);

/** Import a private key in DER format.
 * Returns: 1 if a private key was extracted.
 * Args: ctx:        pointer to a context object (cannot be NULL).
 * Out:  seckey:     pointer to a 32-byte array for storing the private key.
 *                   (cannot be NULL).
 * In:   privkey:    pointer to a private key in DER format (cannot be NULL).
 *       privkeylen: length of the DER private key pointed to be privkey.
 *
 * This function will accept more than just strict DER, and even allow some BER
 * violations. The public key stored inside the DER-encoded private key is not
 * verified for correctness, nor are the curve parameters. Use this function
 * only if you know in advance it is supposed to contain a secp256k1 private
 * key.
 */
static SECP256K1_WARN_UNUSED_RESULT int secp256k1_ec_privkey_import_der(
    const secp256k1_context* ctx,
    unsigned char *seckey,
    const unsigned char *privkey,
    size_t privkeylen
) SECP256K1_ARG_NONNULL(1) SECP256K1_ARG_NONNULL(2) SECP256K1_ARG_NONNULL(3);

static int secp256k1_ec_privkey_import_der(const secp256k1_context* ctx, unsigned char *out32, const unsigned char *privkey, size_t privkeylen) {
    const unsigned char *end = privkey + privkeylen;
    int lenb = 0;
    int len = 0;
    memset(out32, 0, 32);
    /* sequence header */
    if (end < privkey+1 || *privkey != 0x30) {
        return 0;
    }
    privkey++;
    /* sequence length constructor */
    if (end < privkey+1 || !(*privkey & 0x80)) {
        return 0;
    }
    lenb = *privkey & ~0x80; privkey++;
    if (lenb < 1 || lenb > 2) {
        return 0;
    }
    if (end < privkey+lenb) {
        return 0;
    }
    /* sequence length */
    len = privkey[lenb-1] | (lenb > 1 ? privkey[lenb-2] << 8 : 0);
    privkey += lenb;
    if (end < privkey+len) {
        return 0;
    }
    /* sequence element 0: version number (=1) */
    if (end < privkey+3 || privkey[0] != 0x02 || privkey[1] != 0x01 || privkey[2] != 0x01) {
        return 0;
    }
    privkey += 3;
    /* sequence element 1: octet string, up to 32 bytes */
    if (end < privkey+2 || privkey[0] != 0x04 || privkey[1] > 0x20 || end < privkey+2+privkey[1]) {
        return 0;
    }
    memcpy(out32 + 32 - privkey[1], privkey + 2, privkey[1]);
    if (!secp256k1_ec_seckey_verify(ctx, out32)) {
        memset(out32, 0, 32);
        return 0;
    }
    return 1;
}

static int secp256k1_ec_privkey_export_der(const secp256k1_context *ctx, unsigned char *privkey, size_t *privkeylen, const unsigned char *key32, int compressed) {
    secp256k1_pubkey pubkey;
    size_t pubkeylen = 0;
    if (!secp256k1_ec_pubkey_create(ctx, &pubkey, key32)) {
        *privkeylen = 0;
        return 0;
    }
    if (compressed) {
        static const unsigned char begin[] = {
            0x30,0x81,0xD3,0x02,0x01,0x01,0x04,0x20
        };
        static const unsigned char middle[] = {
            0xA0,0x81,0x85,0x30,0x81,0x82,0x02,0x01,0x01,0x30,0x2C,0x06,0x07,0x2A,0x86,0x48,
            0xCE,0x3D,0x01,0x01,0x02,0x21,0x00,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
            0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
            0xFF,0xFF,0xFE,0xFF,0xFF,0xFC,0x2F,0x30,0x06,0x04,0x01,0x00,0x04,0x01,0x07,0x04,
            0x21,0x02,0x79,0xBE,0x66,0x7E,0xF9,0xDC,0xBB,0xAC,0x55,0xA0,0x62,0x95,0xCE,0x87,
            0x0B,0x07,0x02,0x9B,0xFC,0xDB,0x2D,0xCE,0x28,0xD9,0x59,0xF2,0x81,0x5B,0x16,0xF8,
            0x17,0x98,0x02,0x21,0x00,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
            0xFF,0xFF,0xFF,0xFF,0xFE,0xBA,0xAE,0xDC,0xE6,0xAF,0x48,0xA0,0x3B,0xBF,0xD2,0x5E,
            0x8C,0xD0,0x36,0x41,0x41,0x02,0x01,0x01,0xA1,0x24,0x03,0x22,0x00
        };
        unsigned char *ptr = privkey;
        memcpy(ptr, begin, sizeof(begin)); ptr += sizeof(begin);
        memcpy(ptr, key32, 32); ptr += 32;
        memcpy(ptr, middle, sizeof(middle)); ptr += sizeof(middle);
        secp256k1_ec_pubkey_serialize(ctx, ptr, &pubkeylen, &pubkey, SECP256K1_EC_COMPRESSED);
        ptr += pubkeylen;
        *privkeylen = ptr - privkey;
    } else {
        static const unsigned char begin[] = {
            0x30,0x82,0x01,0x13,0x02,0x01,0x01,0x04,0x20
        };
        static const unsigned char middle[] = {
            0xA0,0x81,0xA5,0x30,0x81,0xA2,0x02,0x01,0x01,0x30,0x2C,0x06,0x07,0x2A,0x86,0x48,
            0xCE,0x3D,0x01,0x01,0x02,0x21,0x00,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
            0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
            0xFF,0xFF,0xFE,0xFF,0xFF,0xFC,0x2F,0x30,0x06,0x04,0x01,0x00,0x04,0x01,0x07,0x04,
            0x41,0x04,0x79,0xBE,0x66,0x7E,0xF9,0xDC,0xBB,0xAC,0x55,0xA0,0x62,0x95,0xCE,0x87,
            0x0B,0x07,0x02,0x9B,0xFC,0xDB,0x2D,0xCE,0x28,0xD9,0x59,0xF2,0x81,0x5B,0x16,0xF8,
            0x17,0x98,0x48,0x3A,0xDA,0x77,0x26,0xA3,0xC4,0x65,0x5D,0xA4,0xFB,0xFC,0x0E,0x11,
            0x08,0xA8,0xFD,0x17,0xB4,0x48,0xA6,0x85,0x54,0x19,0x9C,0x47,0xD0,0x8F,0xFB,0x10,
            0xD4,0xB8,0x02,0x21,0x00,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
            0xFF,0xFF,0xFF,0xFF,0xFE,0xBA,0xAE,0xDC,0xE6,0xAF,0x48,0xA0,0x3B,0xBF,0xD2,0x5E,
            0x8C,0xD0,0x36,0x41,0x41,0x02,0x01,0x01,0xA1,0x44,0x03,0x42,0x00
        };
        unsigned char *ptr = privkey;
        memcpy(ptr, begin, sizeof(begin)); ptr += sizeof(begin);
        memcpy(ptr, key32, 32); ptr += 32;
        memcpy(ptr, middle, sizeof(middle)); ptr += sizeof(middle);
        secp256k1_ec_pubkey_serialize(ctx, ptr, &pubkeylen, &pubkey, SECP256K1_EC_UNCOMPRESSED);
        ptr += pubkeylen;
        *privkeylen = ptr - privkey;
    }
    return 1;
}

#endif