Squashed 'src/secp256k1/' changes from 22f60a6..2bfb82b

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: 2bfb82b10edf0f0b0e366a12f94c8b21a914159d

4 files changed, 444 insertions, 0 deletions

diff --git a/contrib/lax_der_parsing.c b/contrib/lax_der_parsing.c
new file mode 100644
index 0000000000..5b141a9948
--- /dev/null
+++ 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;
+}
+
diff --git a/contrib/lax_der_parsing.h b/contrib/lax_der_parsing.h
new file mode 100644
index 0000000000..6d27871a7c
--- /dev/null
+++ 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
diff --git a/contrib/lax_der_privatekey_parsing.c b/contrib/lax_der_privatekey_parsing.c
new file mode 100644
index 0000000000..c2e63b4b8d
--- /dev/null
+++ 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;
+}
diff --git a/contrib/lax_der_privatekey_parsing.h b/contrib/lax_der_privatekey_parsing.h
new file mode 100644
index 0000000000..2fd088f8ab
--- /dev/null
+++ 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