what algorithm does bitcoin use

The Bitcoin cryptocurrency uses the SHA-256 (Secure Hash Algorithm 256-bit) algorithm for its proof-of-work system. The algorithm consists of several steps:

1. Message Padding: The input data is padded to ensure its length is a multiple of 512 bits. This padding includes a 1-bit followed by zeros and a 64-bit representation of the original data length.

2. Message Parsing: The padded message is split into 512-bit blocks.

3. Initial Hash Values: The algorithm uses a set of predefined initial hash values, known as the "constants," which are combined with the message blocks.

4. Compression Function: Each message block is processed by a compression function. This function operates on a 256-bit state, known as the "message schedule," which is updated after each block.

5. Rounds: The compression function consists of multiple rounds, where each round performs a series of logical and arithmetic operations on the message schedule.

6. Final Hash: After processing all the blocks, the final state of the compression function is the hash value of the input data.

The SHA-256 algorithm is designed to be a one-way function, meaning that it is computationally infeasible to reverse-engineer the original input from its hash value. This property makes it suitable for applications such as digital signatures and proof-of-work systems like Bitcoin.

Keep in mind that the explanation provided here is a simplified overview of the algorithm. The actual implementation of SHA-256 involves more intricate details and optimizations.