Add SHA256 counter tests

Those tests verify that the SHA256 bit counter wraps correctly at bit lengths
20 to 34. This wide range aims at being independent of the implementation of the
counter and it catches multiple natural 32-bit overflows (e.g., counting bits,
counting bytes, counting blocks, ...).

The test vectors have been generated using
cloudtools/sha256@e0645d1
and the following Python script

```
from sha256 import sha256
from copy import copy

def midstate_c_definition(hasher):
    ret  = '    {{UINT32_C(0x' + hasher.state[0].hex('_', 4).replace('_', '), UINT32_C(0x') + ')},\n'
    ret += '    {0x00}, UINT64_C(' + str(hasher.state[1]) + ')}'
    return ret

def output_c_literal(hasher):
    return '{0x' + hasher.digest().hex('_').replace('_', ', 0x') + '}'

MESSAGE = b'abcdefghbcdefghicdefghijdefghijkefghijklfghijklmghijklmnhijklmno'
ITER_BOUNDARIES = [(2**b)//len(MESSAGE) - 1 for b in range(20, 34)]

midstates = []
digests = []
hasher = sha256()
for i in range(ITER_BOUNDARIES[-1] + 1):
    if i in ITER_BOUNDARIES:
        midstates.append(midstate_c_definition(hasher))
        hasher_copy = copy(hasher)
        hasher_copy.update(MESSAGE)
        digests.append(output_c_literal(hasher_copy))
    hasher.update(MESSAGE)

for x in midstates:
    print(x + ',')

for x in digests:
    print(x + ',')
```

Author: real-or-random

src/tests.c

@@ -463,6 +463,65 @@ void run_sha256_tests(void) {
     }
 }
 
+void run_sha256_counter_tests(void) {
+    static const char *input = "abcdefghbcdefghicdefghijdefghijkefghijklfghijklmghijklmnhijklmno";
+    static const secp256k1_sha256 midstates[14] = {
+        {{UINT32_C(0xa2b5c8bb), UINT32_C(0x26c88bb3), UINT32_C(0x2abdc3d2), UINT32_C(0x9def99a3), UINT32_C(0xdfd21a6e), UINT32_C(0x41fe585b), UINT32_C(0x7ef2c440), UINT32_C(0x2b79adda)},
+         {0x00}, UINT64_C(1048512)},
+        {{UINT32_C(0xa0d29445), UINT32_C(0x9287de66), UINT32_C(0x76aabd71), UINT32_C(0x41acd765), UINT32_C(0x0c7528b4), UINT32_C(0x84e14906), UINT32_C(0x942faec6), UINT32_C(0xcc5a7b26)},
+         {0x00}, UINT64_C(2097088)},
+        {{UINT32_C(0x50449526), UINT32_C(0xb9f1d657), UINT32_C(0xa0fc13e9), UINT32_C(0x50860f10), UINT32_C(0xa550c431), UINT32_C(0x3fbc97c1), UINT32_C(0x7bbb2d89), UINT32_C(0xdb67bac1)},
+         {0x00}, UINT64_C(4194240)},
+        {{UINT32_C(0x54a6efdc), UINT32_C(0x46762e7b), UINT32_C(0x88bfe73f), UINT32_C(0xbbd149c7), UINT32_C(0x41620c43), UINT32_C(0x1168da7b), UINT32_C(0x2c5960f9), UINT32_C(0xeccffda6)},
+         {0x00}, UINT64_C(8388544)},
+        {{UINT32_C(0x2515a8f5), UINT32_C(0x5faa2977), UINT32_C(0x3a850486), UINT32_C(0xac858cad), UINT32_C(0x7b7276ee), UINT32_C(0x235c0385), UINT32_C(0xc53a157c), UINT32_C(0x7cb3e69c)},
+         {0x00}, UINT64_C(16777152)},
+        {{UINT32_C(0x34f39828), UINT32_C(0x409fedb7), UINT32_C(0x4bbdd0fb), UINT32_C(0x3b643634), UINT32_C(0x7806bf2e), UINT32_C(0xe0d1b713), UINT32_C(0xca3f2e1e), UINT32_C(0xe38722c2)},
+         {0x00}, UINT64_C(33554368)},
+        {{UINT32_C(0x389ef5c5), UINT32_C(0x38c54167), UINT32_C(0x8f5d56ab), UINT32_C(0x582a75cc), UINT32_C(0x8217caef), UINT32_C(0xf10947dd), UINT32_C(0x6a1998a8), UINT32_C(0x048f0b8c)},
+         {0x00}, UINT64_C(67108800)},
+        {{UINT32_C(0xd6c3f394), UINT32_C(0x0bee43b9), UINT32_C(0x6783f497), UINT32_C(0x29fa9e21), UINT32_C(0x6ce491c1), UINT32_C(0xa81fe45e), UINT32_C(0x2fc3859a), UINT32_C(0x269012d0)},
+         {0x00}, UINT64_C(134217664)},
+        {{UINT32_C(0x6dd3c526), UINT32_C(0x44d88aa0), UINT32_C(0x806a1bae), UINT32_C(0xfbcc0d32), UINT32_C(0x9d6144f3), UINT32_C(0x9d2bd757), UINT32_C(0x9851a957), UINT32_C(0xb50430ad)},
+         {0x00}, UINT64_C(268435392)},
+        {{UINT32_C(0x2add4021), UINT32_C(0xdfe8a9e6), UINT32_C(0xa56317c6), UINT32_C(0x7a15f5bb), UINT32_C(0x4a48aacd), UINT32_C(0x5d368414), UINT32_C(0x4f00e6f0), UINT32_C(0xd9355023)},
+         {0x00}, UINT64_C(536870848)},
+        {{UINT32_C(0xb66666b4), UINT32_C(0xdbeac32b), UINT32_C(0x0ea351ae), UINT32_C(0xcba9da46), UINT32_C(0x6278b874), UINT32_C(0x8c508e23), UINT32_C(0xe16ca776), UINT32_C(0x8465bac1)},
+         {0x00}, UINT64_C(1073741760)},
+        {{UINT32_C(0xb6744789), UINT32_C(0x9cce87aa), UINT32_C(0xc4c478b7), UINT32_C(0xf38404d8), UINT32_C(0x2e38ba62), UINT32_C(0xa3f7019b), UINT32_C(0x50458fe7), UINT32_C(0x3047dbec)},
+         {0x00}, UINT64_C(2147483584)},
+        {{UINT32_C(0x8b1297ba), UINT32_C(0xba261a80), UINT32_C(0x2ba1b0dd), UINT32_C(0xfbc67d6d), UINT32_C(0x61072c4e), UINT32_C(0x4b5a2a0f), UINT32_C(0x52872760), UINT32_C(0x2dfeb162)},
+         {0x00}, UINT64_C(4294967232)},
+        {{UINT32_C(0x24f33cf7), UINT32_C(0x41ad6583), UINT32_C(0x41c8ff5d), UINT32_C(0xca7ef35f), UINT32_C(0x50395756), UINT32_C(0x021b743e), UINT32_C(0xd7126cd7), UINT32_C(0xd037473a)},
+         {0x00}, UINT64_C(8589934528)}
+    };
+    static const unsigned char outputs[14][32] = {
+        {0x0e, 0x83, 0xe2, 0xc9, 0x4f, 0xb2, 0xb8, 0x2b, 0x89, 0x06, 0x92, 0x78, 0x04, 0x03, 0x48, 0x5c, 0x48, 0x44, 0x67, 0x61, 0x77, 0xa4, 0xc7, 0x90, 0x9e, 0x92, 0x55, 0x10, 0x05, 0xfe, 0x39, 0x15},
+        {0x1d, 0x1e, 0xd7, 0xb8, 0xa3, 0xa7, 0x8a, 0x79, 0xfd, 0xa0, 0x05, 0x08, 0x9c, 0xeb, 0xf0, 0xec, 0x67, 0x07, 0x9f, 0x8e, 0x3c, 0x0d, 0x8e, 0xf9, 0x75, 0x55, 0x13, 0xc1, 0xe8, 0x77, 0xf8, 0xbb},
+        {0x66, 0x95, 0x6c, 0xc9, 0xe0, 0x39, 0x65, 0xb6, 0xb0, 0x05, 0xd1, 0xaf, 0xaf, 0xf3, 0x1d, 0xb9, 0xa4, 0xda, 0x6f, 0x20, 0xcd, 0x3a, 0xae, 0x64, 0xc2, 0xdb, 0xee, 0xf5, 0xb8, 0x8d, 0x57, 0x0e},
+        {0x3c, 0xbb, 0x1c, 0x12, 0x5e, 0x17, 0xfd, 0x54, 0x90, 0x45, 0xa7, 0x7b, 0x61, 0x6c, 0x1d, 0xfe, 0xe6, 0xcc, 0x7f, 0xee, 0xcf, 0xef, 0x33, 0x35, 0x50, 0x62, 0x16, 0x70, 0x2f, 0x87, 0xc3, 0xc9},
+        {0x53, 0x4d, 0xa8, 0xe7, 0x1e, 0x98, 0x73, 0x8d, 0xd9, 0xa3, 0x54, 0xa5, 0x0e, 0x59, 0x2c, 0x25, 0x43, 0x6f, 0xaa, 0xa2, 0xf5, 0x21, 0x06, 0x3e, 0xc9, 0x82, 0x06, 0x94, 0x98, 0x72, 0x9d, 0xa7},
+        {0xef, 0x7e, 0xe9, 0x6b, 0xd3, 0xe5, 0xb7, 0x41, 0x4c, 0xc8, 0xd3, 0x07, 0x52, 0x9a, 0x5a, 0x8b, 0x4e, 0x1e, 0x75, 0xa4, 0x17, 0x78, 0xc8, 0x36, 0xcd, 0xf8, 0x2e, 0xd9, 0x57, 0xe3, 0xd7, 0x07},
+        {0x87, 0x16, 0xfb, 0xf9, 0xa5, 0xf8, 0xc4, 0x56, 0x2b, 0x48, 0x52, 0x8e, 0x2d, 0x30, 0x85, 0xb6, 0x4c, 0x56, 0xb5, 0xd1, 0x16, 0x9c, 0xcf, 0x32, 0x95, 0xad, 0x03, 0xe8, 0x05, 0x58, 0x06, 0x76},
+        {0x75, 0x03, 0x80, 0x28, 0xf2, 0xa7, 0x63, 0x22, 0x1a, 0x26, 0x9c, 0x68, 0xe0, 0x58, 0xfc, 0x73, 0xeb, 0x42, 0xf6, 0x86, 0x16, 0x24, 0x4b, 0xbc, 0x24, 0xf7, 0x02, 0xc8, 0x3d, 0x90, 0xe2, 0xb0},
+        {0xdf, 0x49, 0x0f, 0x15, 0x7b, 0x7d, 0xbf, 0xe0, 0xd4, 0xcf, 0x47, 0xc0, 0x80, 0x93, 0x4a, 0x61, 0xaa, 0x03, 0x07, 0x66, 0xb3, 0x38, 0x5d, 0xc8, 0xc9, 0x07, 0x61, 0xfb, 0x97, 0x10, 0x2f, 0xd8},
+        {0x77, 0x19, 0x40, 0x56, 0x41, 0xad, 0xbc, 0x59, 0xda, 0x1e, 0xc5, 0x37, 0x14, 0x63, 0x7b, 0xfb, 0x79, 0xe2, 0x7a, 0xb1, 0x55, 0x42, 0x99, 0x42, 0x56, 0xfe, 0x26, 0x9d, 0x0f, 0x7e, 0x80, 0xc6},
+        {0x50, 0xe7, 0x2a, 0x0e, 0x26, 0x44, 0x2f, 0xe2, 0x55, 0x2d, 0xc3, 0x93, 0x8a, 0xc5, 0x86, 0x58, 0x22, 0x8c, 0x0c, 0xbf, 0xb1, 0xd2, 0xca, 0x87, 0x2a, 0xe4, 0x35, 0x26, 0x6f, 0xcd, 0x05, 0x5e},
+        {0xe4, 0x80, 0x6f, 0xdb, 0x3d, 0x7d, 0xba, 0xde, 0x50, 0x3f, 0xea, 0x00, 0x3d, 0x46, 0x59, 0x64, 0xfd, 0x58, 0x1c, 0xa1, 0xb8, 0x7d, 0x5f, 0xac, 0x94, 0x37, 0x9e, 0xa0, 0xc0, 0x9c, 0x93, 0x8b},
+        {0x2c, 0xf3, 0xa9, 0xf6, 0x15, 0x25, 0x80, 0x70, 0x76, 0x99, 0x7d, 0xf1, 0xc3, 0x2f, 0xa3, 0x31, 0xff, 0x92, 0x35, 0x2e, 0x8d, 0x04, 0x13, 0x33, 0xd8, 0x0d, 0xdb, 0x4a, 0xf6, 0x8c, 0x03, 0x34},
+        {0xec, 0x12, 0x24, 0x9f, 0x35, 0xa4, 0x29, 0x8b, 0x9e, 0x4a, 0x95, 0xf8, 0x61, 0xaf, 0x61, 0xc5, 0x66, 0x55, 0x3e, 0x3f, 0x2a, 0x98, 0xea, 0x71, 0x16, 0x6b, 0x1c, 0xd9, 0xe4, 0x09, 0xd2, 0x8e}
+    };
+    unsigned int i;
+    for (i = 0; i < sizeof(midstates)/sizeof(midstates[0]); i++) {
+        unsigned char out[32];
+        secp256k1_sha256 hasher;
+        secp256k1_sha256_initialize_midstate(&hasher, &midstates[i]);
+        secp256k1_sha256_write(&hasher, (const unsigned char*)input, strlen(input));
+        secp256k1_sha256_finalize(&hasher, out);
+        CHECK(memcmp(out, outputs[i], 32) == 0);
+    }
+}
+
 void run_hmac_sha256_tests(void) {
     static const char *keys[6] = {
         "\x0b\x0b\x0b\x0b\x0b\x0b\x0b\x0b\x0b\x0b\x0b\x0b\x0b\x0b\x0b\x0b\x0b\x0b\x0b\x0b",
@@ -5269,6 +5328,7 @@ int main(int argc, char **argv) {
     run_rand_int();
 
     run_sha256_tests();
+    run_sha256_counter_tests();
     run_hmac_sha256_tests();
     run_rfc6979_hmac_sha256_tests();