Litecoin is a fork of the bitcoin source code released in 2011. It uses Scrypt as PoW, originally introduced in the Tenebrix coin. Litecoin allows for faster transactions as compared to bitcoin due to its faster block generation time of 2.5 minutes. Also difficulty readjustment is achieved every 3.5 days roughly due to faster block generation time. The total coin supply is 84 million.
Scrypt is a sequentially memory hard function that is the first alternative to the SHA-256-based PoW algorithm. It was originally proposed as a password-based key derivation function PBKDF. The key idea is that if the function requires large number of memory to run then custom hardware such as ASICs will require more VLSI area, which would be unfeasible to build. The Scrypt algorithm requires a large array of pseudo random bits to be held in memory and a key is derived from this in a pseudo random fashion. The algorithm is based on a phenomenon called Time-Memory Tradeoff (TMTO). If memory requirements...