Squashed 'src/secp256k1/' changes from 22f60a6..84973d3

84973d3 Merge #454: Remove residual parts from the schnorr expirement. 5e95bf2 Remove residual parts from the schnorr expirement. cbc20b8 Merge #452: Minor optimizations to _scalar_inverse to save 4M 4cc8f52 Merge #437: Unroll secp256k1_fe_(get|set)_b32 to make them much faster. 465159c Further shorten the addition chain for scalar inversion. a2b6b19 Fix benchmark print_number infinite loop. 8b7680a Unroll secp256k1_fe_(get|set)_b32 for 10x26. aa84990 Unroll secp256k1_fe_(get|set)_b32 for 5x52. cf12fa1 Minor optimizations to _scalar_inverse to save 4M 1199492 Merge #408: Add `secp256k1_ec_pubkey_negate` and `secp256k1_ec_privkey_negate` 6af0871 Merge #441: secp256k1_context_randomize: document. ab31a52 Merge #444: test: Use checked_alloc eda5c1a Merge #449: Remove executable bit from secp256k1.c 51b77ae Remove executable bit from secp256k1.c 5eb030c test: Use checked_alloc 72d952c FIXUP: Missing "is" 70ff29b secp256k1_context_randomize: document. 9d560f9 Merge #428: Exhaustive recovery 8e48aa6 Add `secp256k1_ec_pubkey_negate` and `secp256k1_ec_privkey_negate` 2cee5fd exhaustive tests: add recovery module 8225239 Merge #433: Make the libcrypto detection fail the newer API. 12de863 Make the libcrypto detection fail the newer API. 678b0e5 exhaustive tests: remove erroneous comment from ecdsa_sig_sign 2928420 Merge #427: Remove Schnorr from travis as well 03ff8c2 group_impl.h: remove unused `secp256k1_ge_set_infinity` function a724d72 configure: add --enable-coverage to set options for coverage analysis b595163 recovery: add tests to cover API misusage 8eecc4a Remove Schnorr from travis as well 6f8ae2f ecdh: test NULL-checking of arguments 25e3cfb ecdsa_impl: replace scalar if-checks with VERIFY_CHECKs in ecdsa_sig_sign a8abae7 Merge #310: Add exhaustive test for group functions on a low-order subgroup b4ceedf Add exhaustive test for verification 83836a9 Add exhaustive tests for group arithmetic, signing, and ecmult on a small group 20b8877 Add exhaustive test for group functions on a low-order subgroup 80773a6 Merge #425: Remove Schnorr experiment e06e878 Remove Schnorr experiment 04c8ef3 Merge #407: Modify parameter order of internal functions to match API parameter order 6e06696 Merge #411: Remove guarantees about memcmp-ability 40c8d7e Merge #421: Update scalar_4x64_impl.h a922365 Merge #422: Restructure nonce clearing 3769783 Restructure nonce clearing 0f9e69d Restructure nonce clearing 9d67afa Update scalar_4x64_impl.h 7d15cd7 Merge #413: fix auto-enabled static precompuatation 00c5d2e fix auto-enabled static precompuatation 91219a1 Remove guarantees about memcmp-ability 7a49cac Merge #410: Add string.h include to ecmult_impl 0bbd5d4 Add string.h include to ecmult_impl 353c1bf Fix secp256k1_ge_set_table_gej_var parameter order 541b783 Fix secp256k1_ge_set_all_gej_var parameter order 7d893f4 Fix secp256k1_fe_inv_all_var parameter order c5b32e1 Merge #405: Make secp256k1_fe_sqrt constant time 926836a Make secp256k1_fe_sqrt constant time e2a8e92 Merge #404: Replace 3M + 4S doubling formula with 2M + 5S one 8ec49d8 Add note about 2M + 5S doubling formula 5a91bd7 Merge #400: A couple minor cleanups ac01378 build: add -DSECP256K1_BUILD to benchmark_internal build flags a6c6f99 Remove a bunch of unused stdlib #includes 65285a6 Merge #403: configure: add flag to disable OpenSSL tests a9b2a5d configure: add flag to disable OpenSSL tests b340123 Merge #402: Add support for testing quadratic residues e6e9805 Add function for testing quadratic residue field/group elements. efd953a Add Jacobi symbol test via GMP fa36a0d Merge #401: ecmult_const: unify endomorphism and non-endomorphism skew cases c6191fd ecmult_const: unify endomorphism and non-endomorphism skew cases 0b3e618 Merge #378: .gitignore build-aux cleanup 6042217 Merge #384: JNI: align shared files copyright/comments to bitcoinj's 24ad20f Merge #399: build: verify that the native compiler works for static precomp b3be852 Merge #398: Test whether ECDH and Schnorr are enabled for JNI aa0b1fd build: verify that the native compiler works for static precomp eee808d Test whether ECDH and Schnorr are enabled for JNI 7b0fb18 Merge #366: ARM assembly implementation of field_10x26 inner (rebase of #173) 001f176 ARM assembly implementation of field_10x26 inner 0172be9 Merge #397: Small fixes for sha256 3f8b78e Fix undefs in hash_impl.h 2ab4695 Fix state size in sha256 struct 6875b01 Merge #386: Add some missing `VERIFY_CHECK(ctx != NULL)` 2c52b5d Merge #389: Cast pointers through uintptr_t under JNI 43097a4 Merge #390: Update bitcoin-core GitHub links 31c9c12 Merge #391: JNI: Only call ecdsa_verify if its inputs parsed correctly 1cb2302 Merge #392: Add testcase which hits additional branch in secp256k1_scalar_sqr d2ee340 Merge #388: bench_ecdh: fix call to secp256k1_context_create 093a497 Add testcase which hits additional branch in secp256k1_scalar_sqr a40c701 JNI: Only call ecdsa_verify if its inputs parsed correctly faa2a11 Update bitcoin-core GitHub links 47b9e78 Cast pointers through uintptr_t under JNI f36f9c6 bench_ecdh: fix call to secp256k1_context_create bcc4881 Add some missing `VERIFY_CHECK(ctx != NULL)` for functions that use `ARG_CHECK` 6ceea2c align shared files copyright/comments to bitcoinj's 70141a8 Update .gitignore 7b549b1 Merge #373: build: fix x86_64 asm detection for some compilers bc7c93c Merge #374: Add note about y=0 being possible on one of the sextic twists e457018 Merge #364: JNI rebased 86e2d07 JNI library: cleanup, removed unimplemented code 3093576a JNI library bd2895f Merge pull request #371 e72e93a Add note about y=0 being possible on one of the sextic twists 3f8fdfb build: fix x86_64 asm detection for some compilers e5a9047 [Trivial] Remove double semicolons c18b869 Merge pull request #360 3026daa Merge pull request #302 03d4611 Add sage verification script for the group laws a965937 Merge pull request #361 83221ec Add experimental features to configure 5d4c5a3 Prevent damage_array in the signature test from going out of bounds. 419bf7f Merge pull request #356 6c527ec Merge pull request #357 445f7f1 Fix for Windows compile issue 03d84a4 Benchmark against OpenSSL verification 2bfb82b Merge pull request #351 06aeea5 Turn secp256k1_ec_pubkey_serialize outlen to in/out 970164d Merge pull request #348 6466625 Improvements for coordinate decompression e2100ad Merge pull request #347 8e48787 Change secp256k1_ec_pubkey_combine's count argument to size_t. c69dea0 Clear output in more cases for pubkey_combine, adds tests. 269d422 Comment copyediting. b4d17da Merge pull request #344 4709265 Merge pull request #345 26abce7 Adds 32 static test vectors for scalar mul, sqr, inv. 5b71a3f Better error case handling for pubkey_create & pubkey_serialize, more tests. 3b7bc69 Merge pull request #343 eed87af Change contrib/laxder from headers-only to files compilable as standalone C d7eb1ae Merge pull request #342 7914a6e Make lax_der_privatekey_parsing.h not depend on internal code 73f64ff Merge pull request #339 9234391 Overhaul flags handling 1a36898 Make flags more explicit, add runtime checks. 1a3e03a Merge pull request #340 96be204 Add additional tests for eckey and arg-checks. bb5aa4d Make the tweak function zeroize-output-on-fail behavior consistent. 4a243da Move secp256k1_ec_privkey_import/export to contrib. 1b3efc1 Move secp256k1_ecdsa_sig_recover into the recovery module. e3cd679 Eliminate all side-effects from VERIFY_CHECK() usage. b30fc85 Avoid nonce_function_rfc6979 algo16 argument emulation. 70d4640 Make secp256k1_ec_pubkey_create skip processing invalid secret keys. 6c476a8 Minor comment improvements. 131afe5 Merge pull request #334 0c6ab2f Introduce explicit lower-S normalization fea19e7 Add contrib/lax_der_parsing.h 3bb9c44 Rewrite ECDSA signature parsing code fa57f1b Use secp256k1_rand_int and secp256k1_rand_bits more 49b3749 Add new tests for the extra testrand functions f684d7d Faster secp256k1_rand_int implementation 251b1a6 Improve testrand: add extra random functions 31994c8 Merge pull request #338 f79aa88 Bugfix: swap arguments to noncefp c98df26 Merge pull request #319 67f7da4 Extensive interface and operations tests for secp256k1_ec_pubkey_parse. ee2cb40 Add ARG_CHECKs to secp256k1_ec_pubkey_parse/secp256k1_ec_pubkey_serialize 7450ef1 Merge pull request #328 68a3c76 Merge pull request #329 98135ee Merge pull request #332 37100d7 improve ECDH header-doc b13d749 Fix couple of typos in API comments 7c823e3 travis: fixup module configs cc3141a Merge pull request #325 ee58fae Merge pull request #326 213aa67 Do not force benchmarks to be statically linked. 338fc8b Add API exports to secp256k1_nonce_function_default and secp256k1_nonce_function_rfc6979. 52fd03f Merge pull request #320 9f6993f Remove some dead code. 357f8cd Merge pull request #314 118cd82 Use explicit symbol visibility. 4e64608 Include public module headers when compiling modules. 1f41437 Merge pull request #316 fe0d463 Merge pull request #317 cfe0ed9 Fix miscellaneous style nits that irritate overactive static analysis. 2b199de Use the explicit NULL macro for pointer comparisons. 9e90516 Merge pull request #294 dd891e0 Get rid of _t as it is POSIX reserved 201819b Merge pull request #313 912f203 Eliminate a few unbraced statements that crept into the code. eeab823 Merge pull request #299 486b9bb Use a flags bitfield for compressed option to secp256k1_ec_pubkey_serialize and secp256k1_ec_privkey_export 05732c5 Callback data: Accept pointers to either const or non-const data 1973c73 Bugfix: Reinitialise buffer lengths that have been used as outputs 788038d Use size_t for lengths (at least in external API) c9d7c2a secp256k1_context_set_{error,illegal}_callback: Restore default handler by passing NULL as function argument 9aac008 secp256k1_context_destroy: Allow NULL argument as a no-op 64b730b secp256k1_context_create: Use unsigned type for flags bitfield cb04ab5 Merge pull request #309 a551669 Merge pull request #295 81e45ff Update group_impl.h 85e3a2c Merge pull request #112 b2eb63b Merge pull request #293 dc0ce9f [API BREAK] Change argument order to out/outin/in 6d947ca Merge pull request #298 c822693 Merge pull request #301 6d04350 Merge pull request #303 7ab311c Merge pull request #304 5fb3229 Fixes a bug where bench_sign would fail due to passing in too small a buffer. 263dcbc remove unused assignment b183b41 bugfix: "ARG_CHECK(ctx != NULL)" makes no sense 6da1446 build: fix parallel build 5eb4356 Merge pull request #291 c996d53 Print success 9f443be Move pubkey recovery code to separate module d49abbd Separate ECDSA recovery tests 439d34a Separate recoverable and normal signatures a7b046e Merge pull request #289 f66907f Improve/reformat API documentation secp256k1.h 2f77487 Add context building benchmarks cc623d5 Merge pull request #287 de7e398 small typo fix 9d96e36 Merge pull request #280 432e1ce Merge pull request #283 14727fd Use correct name in gitignore 356b0e9 Actually test static precomputation in Travis ff3a5df Merge pull request #284 2587208 Merge pull request #212 a5a66c7 Add support for custom EC-Schnorr-SHA256 signatures d84a378 Merge pull request #252 72ae443 Improve perf. of cmov-based table lookup 92e53fc Implement endomorphism optimization for secp256k1_ecmult_const ed35d43 Make `secp256k1_scalar_add_bit` conditional; make `secp256k1_scalar_split_lambda_var` constant time 91c0ce9 Add benchmarks for ECDH and const-time multiplication 0739bbb Add ECDH module which works by hashing the output of ecmult_const 4401500 Add constant-time multiply `secp256k1_ecmult_const` for ECDH e4ce393 build: fix hard-coded usage of "gen_context" b8e39ac build: don't use BUILT_SOURCES for the static context header baa75da tests: add a couple tests ae4f0c6 Merge pull request #278 995c548 Introduce callback functions for dealing with errors. c333074 Merge pull request #282 18c329c Remove the internal secp256k1_ecdsa_sig_t type 74a2acd Add a secp256k1_ecdsa_signature_t type 23cfa91 Introduce secp256k1_pubkey_t type 4c63780 Merge pull request #269 3e6f1e2 Change rfc6979 implementation to be a generic PRNG ed5334a Update configure.ac to make it build on OpenBSD 1b68366 Merge pull request #274 a83bb48 Make ecmult static precomputation default 166b32f Merge pull request #276 c37812f Add gen_context src/ecmult_static_context.h to CLEANFILES to fix distclean. 125c15d Merge pull request #275 76f6769 Fix build with static ecmult altroot and make dist. 5133f78 Merge pull request #254 b0a60e6 Merge pull request #258 733c1e6 Add travis build to test the static context. fbecc38 Add ability to use a statically generated ecmult context. 4fb174d Merge pull request #263 4ab8990 Merge pull request #270 bdf0e0c Merge pull request #271 31d0c1f Merge pull request #273 eb2c8ff Add missing casts to SECP256K1_FE_CONST_INNER 55399c2 Further performance improvements to _ecmult_wnaf 99fd963 Add secp256k1_ec_pubkey_compress(), with test similar to the related decompress() function. 145cc6e Improve performance of _ecmult_wnaf 36b305a Verify the result of GMP modular inverse using non-GMP code 0cbc860 Merge pull request #266 06ff7fe Merge pull request #267 5a43124 Save 1 _fe_negate since s1 == -s2 a5d796e Update code comments 3f3964e Add specific VERIFY tests for _fe_cmov 7d054cd Refactor to save a _fe_negate b28d02a Refactor to remove a local var 55e7fc3 Perf. improvement in _gej_add_ge a0601cd Fix VERIFY calculations in _fe_cmov methods 17f7148 Merge pull request #261 7657420 Add tests for adding P+Q with P.x!=Q.x and P.y=-Q.y 8c5d5f7 tests: Add failing unit test for #257 (bad addition formula) 5de4c5d gej_add_ge: fix degenerate case when computing P + (-lambda)P bcf2fcf gej_add_ge: rearrange algebra e2a07c7 Fix compilation with C++ 873a453 Merge pull request #250 91eb0da Merge pull request #247 210ffed Use separate in and out pointers in `secp256k1_ec_pubkey_decompress` a1d5ae1 Tiny optimization 729badf Merge pull request #210 2d5a186 Apply effective-affine trick to precomp 4f9791a Effective affine addition in EC multiplication 2b4cf41 Use pkg-config always when possible, with failover to manual checks for libcrypto git-subtree-dir: src/secp256k1 git-subtree-split: 84973d393ac240a90b2e1a6538c5368202bc2224
2017-06-06 17:49:31 +12:00
parent a591d98c32
commit 77404203ee
80 changed files with 11846 additions and 2240 deletions
--- a/contrib/lax_der_parsing.c
+++ b/contrib/lax_der_parsing.c
@@ -0,0 +1,150 @@
+/**********************************************************************
+ * 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.*
+ **********************************************************************/
+
+#include <string.h>
+#include <secp256k1.h>
+
+#include "lax_der_parsing.h"
+
+int ecdsa_signature_parse_der_lax(const secp256k1_context* ctx, secp256k1_ecdsa_signature* sig, const unsigned char *input, size_t inputlen) {
+    size_t rpos, rlen, spos, slen;
+    size_t pos = 0;
+    size_t lenbyte;
+    unsigned char tmpsig[64] = {0};
+    int overflow = 0;
+
+    /* Hack to initialize sig with a correctly-parsed but invalid signature. */
+    secp256k1_ecdsa_signature_parse_compact(ctx, sig, tmpsig);
+
+    /* Sequence tag byte */
+    if (pos == inputlen || input[pos] != 0x30) {
+        return 0;
+    }
+    pos++;
+
+    /* Sequence length bytes */
+    if (pos == inputlen) {
+        return 0;
+    }
+    lenbyte = input[pos++];
+    if (lenbyte & 0x80) {
+        lenbyte -= 0x80;
+        if (pos + lenbyte > inputlen) {
+            return 0;
+        }
+        pos += lenbyte;
+    }
+
+    /* Integer tag byte for R */
+    if (pos == inputlen || input[pos] != 0x02) {
+        return 0;
+    }
+    pos++;
+
+    /* Integer length for R */
+    if (pos == inputlen) {
+        return 0;
+    }
+    lenbyte = input[pos++];
+    if (lenbyte & 0x80) {
+        lenbyte -= 0x80;
+        if (pos + lenbyte > inputlen) {
+            return 0;
+        }
+        while (lenbyte > 0 && input[pos] == 0) {
+            pos++;
+            lenbyte--;
+        }
+        if (lenbyte >= sizeof(size_t)) {
+            return 0;
+        }
+        rlen = 0;
+        while (lenbyte > 0) {
+            rlen = (rlen << 8) + input[pos];
+            pos++;
+            lenbyte--;
+        }
+    } else {
+        rlen = lenbyte;
+    }
+    if (rlen > inputlen - pos) {
+        return 0;
+    }
+    rpos = pos;
+    pos += rlen;
+
+    /* Integer tag byte for S */
+    if (pos == inputlen || input[pos] != 0x02) {
+        return 0;
+    }
+    pos++;
+
+    /* Integer length for S */
+    if (pos == inputlen) {
+        return 0;
+    }
+    lenbyte = input[pos++];
+    if (lenbyte & 0x80) {
+        lenbyte -= 0x80;
+        if (pos + lenbyte > inputlen) {
+            return 0;
+        }
+        while (lenbyte > 0 && input[pos] == 0) {
+            pos++;
+            lenbyte--;
+        }
+        if (lenbyte >= sizeof(size_t)) {
+            return 0;
+        }
+        slen = 0;
+        while (lenbyte > 0) {
+            slen = (slen << 8) + input[pos];
+            pos++;
+            lenbyte--;
+        }
+    } else {
+        slen = lenbyte;
+    }
+    if (slen > inputlen - pos) {
+        return 0;
+    }
+    spos = pos;
+    pos += slen;
+
+    /* Ignore leading zeroes in R */
+    while (rlen > 0 && input[rpos] == 0) {
+        rlen--;
+        rpos++;
+    }
+    /* Copy R value */
+    if (rlen > 32) {
+        overflow = 1;
+    } else {
+        memcpy(tmpsig + 32 - rlen, input + rpos, rlen);
+    }
+
+    /* Ignore leading zeroes in S */
+    while (slen > 0 && input[spos] == 0) {
+        slen--;
+        spos++;
+    }
+    /* Copy S value */
+    if (slen > 32) {
+        overflow = 1;
+    } else {
+        memcpy(tmpsig + 64 - slen, input + spos, slen);
+    }
+
+    if (!overflow) {
+        overflow = !secp256k1_ecdsa_signature_parse_compact(ctx, sig, tmpsig);
+    }
+    if (overflow) {
+        memset(tmpsig, 0, 64);
+        secp256k1_ecdsa_signature_parse_compact(ctx, sig, tmpsig);
+    }
+    return 1;
+}
+
--- a/contrib/lax_der_parsing.h
+++ b/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
--- a/contrib/lax_der_privatekey_parsing.c
+++ b/contrib/lax_der_privatekey_parsing.c
@@ -0,0 +1,113 @@
+/**********************************************************************
+ * 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.*
+ **********************************************************************/
+
+#include <string.h>
+#include <secp256k1.h>
+
+#include "lax_der_privatekey_parsing.h"
+
+int 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;
+}
+
+int 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);
+        pubkeylen = 33;
+        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);
+        pubkeylen = 65;
+        secp256k1_ec_pubkey_serialize(ctx, ptr, &pubkeylen, &pubkey, SECP256K1_EC_UNCOMPRESSED);
+        ptr += pubkeylen;
+        *privkeylen = ptr - privkey;
+    }
+    return 1;
+}
--- a/contrib/lax_der_privatekey_parsing.h
+++ b/contrib/lax_der_privatekey_parsing.h
@@ -0,0 +1,90 @@
+/**********************************************************************
+ * 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.*
+ **********************************************************************/
+
+/****
+ * 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 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 <secp256k1.h>
+
+# ifdef __cplusplus
+extern "C" {
+# endif
+
+/** 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
+ */
+SECP256K1_WARN_UNUSED_RESULT int 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.
+ */
+SECP256K1_WARN_UNUSED_RESULT int 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);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif