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scrypt

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Litecoin uses the following values for the call to scrypt:

  • N = 1024;
  • r = 1;
  • p = 1;
  • salt is the same 80 bytes as the input
  • output is 256 bits (32 bytes)

scrypt hashing

The source code in C++ for the scrypt hashing function: github: scrypt.cpp

A Java implementation: github: SCrypt.java

Example dbdump of block 29255

./dbdump.py --datadir=/home/mining/.litecoin/ --block 29255
Block height: 29255
BLOCK adf6e2e56df692822f5e064a8b6404a05d67cccd64bc90f57f65b46805e9a54b
Next block: 0000000000000000000000000000000000000000000000000000000000000000
Time: Wed Nov  9 16:15:52 2011 Nonce: 3562614017
nBits: 0x0x1d018ea7
hashMerkleRoot: 0x066b2a758399d5f19b5c6073d09b500d925982adc4b3edd352efe14667a8ca9f
Previous block: 279f6330ccbbb9103b9e3a5350765052081ddbae898f1ef6b8c64f3bcef715f6
1 transactions:
1 tx in, 1 out
TxIn: COIN GENERATED coinbase:04b217bb4e022309
TxOut: value: 50.000000 pubkey: 1HXG8MWvUFNU3pLpQUJueSC4kHcrNepuwC Script: 65:0448...b8cd CHECKSIG

Raw block header: 01000000f615f7ce3b4fc6b8f61e8f89aedb1d0852507650533a9e3b10b9bbcc30639f279fcaa86746e1ef52d3edb3c4ad8259920d509bd073605c9bf1d59983752a6b06b817bb4ea78e011d012d59d4

Python script to check hashing

import hashlib
import ltc_scrypt    # Packaged with litecoin p2pool - https://github.com/coblee/p2pool

header_hex = "01000000f615f7ce3b4fc6b8f61e8f89aedb1d0852507650533a9e3b10b9bbcc30639f279fcaa86746e1ef52d3edb3c4ad8259920d509bd073605c9bf1d59983752a6b06b817bb4ea78e011d012d59d4"
header_bin = header_hex.decode('hex')

hash = hashlib.sha256(hashlib.sha256(header_bin).digest()).digest()
hash.encode('hex_codec')
hash[::-1].encode('hex_codec')    # convert from big-endian to little-endian

scrypt = ltc_scrypt.getPoWHash(header_bin)
scrypt.encode('hex_codec')
scrypt[::-1].encode('hex_codec')    # convert from big-endian to little-endian

After running this script, it will print out these results:
hash = adf6e2e56df692822f5e064a8b6404a05d67cccd64bc90f57f65b46805e9a54b
scrypt = 0000000110c8357966576df46f3b802ca897deb7ad18b12f1c24ecff6386ebd9

You can see that the hash matches the dbdump BLOCK line above. And the scrypt hash is less than the target:
target = 000000018ea70000000000000000000000000000000000000000000000000000

Breakdown of data and header

See Block hashing algorithm
~/litecoind getwork
{
    "midstate" : "40fd268321efcf60e625707d4e31f9deadd13157e228985de8a10a057b98ed4d",
    "data" : "0000000105e9a54b7f65b46864bc90f55d67cccd8b6404a02f5e064a6df69282adf6e2e5f7f953b0632b25b099858b717bb7b24084148cfa841a89f106bc6b655b18d2ed4ebb191a1d018ea700000000000000800000000000000000000000000000000000000000000000000000000000000000000000000000000080020000",
    "hash1" : "00000000000000000000000000000000000000000000000000000000000000000000008000000000000000000000000000000000000000000000000000010000",
    "target" : "0000000000000000000000000000000000000000000000000000a78e01000000"
}

The data field is stored in big-endian format. We need to cover that to little-endian for each of the fields in the data because we can pass it to the hashing function.

Data is broken down to:

  • Version - 00000001 (4 bytes)
  • Previous hash - 05e9a54b7f65b46864bc90f55d67cccd8b6404a02f5e064a6df69282adf6e2e5 (32 bytes)
  • Merkle root - f7f953b0632b25b099858b717bb7b24084148cfa841a89f106bc6b655b18d2ed (32 bytes)
  • Timestamp - 4ebb191a (4 bytes)
  • Bits (target in compact form) - 1d018ea7 (4 bytes)
  • Nonce - 00000000 (4 bytes)

You need covert these from big-endian to little-endian. This is done 2 characters at a time because each byte is represented by 2 hex chars. (each hex char is 4 bits)

  • Version becomes 01000000
  • Previous hash becomes e5e2f6.....a5e905
  • Merkle root becomes edd218...53f9f7
  • Timestamp becomes 1a19bb4e
  • Bits becomes a78e011d
  • And Nonce is a 32-bit integer you choose that will make the Scrypt hash be less than the target.

Remember that you will need to convert the 32-bit nonce to hex and little-endian also. So if you are trying the nonce 2504433986. The hex version is 9546a142 in big-endian and 42a14695 in little-endian.

You then concatenate these little-endian hex strings together to get the header string (80 bytes) you input into scrypt

01000000 e5e2f6.....a5e905 edd218...53f9f7 1a19bb4e a78e011d 42a14695

External links

Portions of this content was copied from the Litecoin wiki under the CC-BY-3.0 license.