Bugfix: _blkmk_b58check: Check that zero-padding on base58check input matches output

This is needed to properly reject addresses with too many or too few prefix/pad '1's.

base58.c

@@ -83,13 +83,21 @@ bool _blkmk_b58tobin(void *bin, size_t binsz, const char *b58, size_t b58sz) {
 	return true;
 }
 
-int _blkmk_b58check(void *bin, size_t binsz) {
+int _blkmk_b58check(void *bin, size_t binsz, const char *base58str) {
 	unsigned char buf[32];
 	unsigned char *binc = bin;
+	unsigned i;
 	if (!_blkmk_dblsha256(buf, bin, binsz - 4))
 		return -2;
 	if (memcmp(&binc[binsz - 4], buf, 4))
 		return -1;
+	
+	// Check number of zeros is correct AFTER verifying checksum (to avoid possibility of accessing base58str beyond the end)
+	for (i = 0; binc[i] == '\0' && base58str[i] == '1'; ++i)
+	{}  // Just finding the end of zeros, nothing to do in loop
+	if (binc[i] == '\0' || base58str[i] == '1')
+		return -3;
+	
 	return binc[0];
 }
 
@@ -101,7 +109,7 @@ size_t blkmk_address_to_script(void *out, size_t outsz, const char *addr) {
 	
 	if (!_blkmk_b58tobin(addrbin, sizeof(addrbin), addr, 0))
 		return 0;
-	addrver = _blkmk_b58check(addrbin, sizeof(addrbin));
+	addrver = _blkmk_b58check(addrbin, sizeof(addrbin), addr);
 	switch (addrver) {
 		case   0:  // Bitcoin pubkey hash
 		case 111:  // Testnet pubkey hash

example.c

@@ -13,16 +13,24 @@
 #include "testinput.c"
 
 void testb58() {
+	int rv;
+	const char *iaddr = "11Baf75Ferj6A7AoN565gCQj9kGWbDMHfN9";
+	const char *addr = &iaddr[1];
 	char bufx[26] = {'\xff'};
 	char *buf = &bufx[1];
-	if (!_blkmk_b58tobin(buf, 25, "1Baf75Ferj6A7AoN565gCQj9kGWbDMHfN9", 0))
+	if (!_blkmk_b58tobin(buf, 25, addr, 0))
 		exit(1);
 	if (bufx[0] != '\xff')
 		exit(2);
 	char cbuf[51];
 	_blkmk_bin2hex(cbuf, buf, 25);
 	printf("Base58 raw data: %s\n", cbuf);
-	printf("Base58 check: %d\n", _blkmk_b58check(buf, 25));
+	assert((rv = _blkmk_b58check(buf, 25, addr)) == 0);
+	printf("Base58 check: %d\n", rv);
+	assert((rv = _blkmk_b58check(buf, 25, &addr[1])) < 0);
+	printf("Base58 check (invalid/    unpadded): %d\n", rv);
+	assert((rv = _blkmk_b58check(buf, 25, iaddr)) < 0);
+	printf("Base58 check (invalid/extra padded): %d\n", rv);
 }
 
 static

private.h

@@ -13,6 +13,6 @@ extern bool _blkmk_hex2bin(void *o, const char *x, size_t len);
 
 // base58.c
 extern bool _blkmk_b58tobin(void *bin, size_t binsz, const char *b58, size_t b58sz);
-extern int _blkmk_b58check(void *bin, size_t binsz);
+extern int _blkmk_b58check(void *bin, size_t binsz, const char *b58);
 
 #endif