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// This is a reference implementation of the proof of work solver in C.
// For security reasons, it is recommended that you read and understand the
// entire program first if you actually want to run it.
//
// You need to have OpenSSL, and link with -lcrypto
#include <openssl/evp.h>
#include <openssl/bio.h>
#include <openssl/buffer.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <stdlib.h>
#include <errno.h>
bool validate_bit_zeros(const unsigned char *bs, unsigned long n)
{
unsigned long q = n / CHAR_BIT;
unsigned char r = n % CHAR_BIT;
for (unsigned long i = 0; i < q; i++) {
if (bs[i] != 0)
return false;
}
if (r > 0) {
unsigned char mask =
(unsigned char)(UCHAR_MAX << (CHAR_BIT - r));
if (bs[q] & mask)
return false;
}
return true;
}
int main(int argc, char **argv)
{
if (argc < 3) {
fprintf(stderr, "usage: %s <base64_data> <difficulty>\n",
argv[0]);
return 1;
}
size_t base64_data_len = strlen(argv[1]);
unsigned char *base64_data = malloc(base64_data_len);
if (!base64_data) {
perror("malloc");
return 1;
}
memcpy(base64_data, argv[1], base64_data_len);
char *endptr = NULL;
errno = 0;
unsigned long difficulty = strtoul(argv[2], &endptr, 10);
if ((difficulty == ULONG_MAX && errno == ERANGE) || *endptr != '\0'
|| difficulty > 256) {
fprintf(stderr, "invalid difficulty value\n");
free(base64_data);
return 1;
}
BIO *b64 = BIO_new(BIO_f_base64());
BIO *bmem = BIO_new_mem_buf(base64_data, (int)base64_data_len);
if (!b64 || !bmem) {
fprintf(stderr, "BIO_new/BIO_new_mem_buf\n");
free(base64_data);
return 1;
}
BIO_set_flags(b64, BIO_FLAGS_BASE64_NO_NL);
b64 = BIO_push(b64, bmem);
size_t decoded_cap = base64_data_len;
unsigned char *decoded = malloc(decoded_cap);
if (!decoded) {
perror("malloc");
BIO_free_all(b64);
free(base64_data);
return 1;
}
int decoded_len = BIO_read(b64, decoded, (int)decoded_cap);
if (decoded_len < 0) {
fprintf(stderr, "BIO_read\n");
BIO_free_all(b64);
free(base64_data);
free(decoded);
return 1;
}
BIO_free_all(b64);
free(base64_data);
EVP_MD_CTX *mdctx = EVP_MD_CTX_new();
if (!mdctx) {
fprintf(stderr, "EVP_MD_CTX_new\n");
free(decoded);
return 1;
}
size_t len = EVP_MD_size(EVP_sha256());
unsigned char digest[len];
size_t next = 0;
while (1) {
if (EVP_DigestInit_ex(mdctx, EVP_sha256(), NULL) != 1) {
fprintf(stderr, "EVP_DigestInit_ex\n");
EVP_MD_CTX_free(mdctx);
free(decoded);
return 1;
}
if (EVP_DigestUpdate(mdctx, decoded, decoded_len) != 1) {
fprintf(stderr, "EVP_DigestUpdate(data)\n");
EVP_MD_CTX_free(mdctx);
free(decoded);
return 1;
}
if (EVP_DigestUpdate(mdctx, &next, sizeof(next)) != 1) {
fprintf(stderr, "EVP_DigestUpdate(next)\n");
EVP_MD_CTX_free(mdctx);
free(decoded);
return 1;
}
if (EVP_DigestFinal_ex(mdctx, digest, NULL) != 1) {
fprintf(stderr, "EVP_DigestFinal_ex\n");
EVP_MD_CTX_free(mdctx);
free(decoded);
return 1;
}
if (validate_bit_zeros(digest, difficulty)) {
break;
}
next++;
if (!next) {
fprintf(stderr, "unsigned integer overflow\n");
EVP_MD_CTX_free(mdctx);
free(decoded);
return 1;
}
}
EVP_MD_CTX_free(mdctx);
free(decoded);
BIO *b64_out = BIO_new(BIO_f_base64());
BIO *bmem_out = BIO_new(BIO_s_mem());
if (!b64_out || !bmem_out) {
fprintf(stderr, "BIO_new\n");
if (b64_out)
BIO_free_all(b64_out);
if (bmem_out)
BIO_free(bmem_out);
return 1;
}
BIO_set_flags(b64_out, BIO_FLAGS_BASE64_NO_NL);
b64_out = BIO_push(b64_out, bmem_out);
if (BIO_write(b64_out, &next, sizeof(next)) < 0) {
fprintf(stderr, "BIO_write\n");
BIO_free_all(b64_out);
return 1;
}
if (BIO_flush(b64_out) < 1) {
fprintf(stderr, "BIO_flush\n");
BIO_free_all(b64_out);
return 1;
}
BUF_MEM *bptr = NULL;
BIO_get_mem_ptr(b64_out, &bptr);
if (!bptr || !bptr->data) {
fprintf(stderr, "BIO_get_mem_ptr\n");
BIO_free_all(b64_out);
return 1;
}
write(STDOUT_FILENO, bptr->data, bptr->length);
write(STDOUT_FILENO, "\n", 1);
BIO_free_all(b64_out);
return 0;
}
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