What is Hashing?

Hashing refers to the method of transforming a message of any length into a fixed-length output, known as a hash value or digest. The input to a hash function can vary widely, encompassing files, passwords, or messages. The resulting output is a unique, fixed-length string of characters that encapsulates the original input.

Hashing algorithms are crafted to yield hash values that exhibit the following characteristics:

• Uniqueness: Different inputs should yield distinct hash values.
• Determinism: The same input must consistently produce the same hash value.
• One-wayness: It should be impossible to retrieve the original input from its hash value.
• Non-invertibility: It should be impractical to discover two different inputs that generate the same hash value.

Hashing is extensively employed in various domains, including password storage, digital signatures, and message authentication codes.

Overview of SHA-256

SHA-256 operates as a one-way, non-invertible hash function that generates a 256-bit hash value. Developed by the National Security Agency (NSA) and introduced in 2001 as part of the SHA-2 family, SHA-256 finds applications in areas such as blockchain technology, digital signatures, and secure password storage.

The SHA-256 algorithm comprises multiple logical operations, including bitwise manipulations, modular arithmetic, and logical processes. The input message is segmented into 512-bit blocks, with each block undergoing a series of rounds. The output from each round serves as input for the subsequent round until the final hash value is achieved.

SHA-256 Algorithm Stages

The SHA-256 algorithm can be broken down into six primary stages: message padding, message parsing, message expansion, compression, output formatting, and the final hash value. Let’s examine each stage in detail.

1. Message Padding

   The original input message is padded with zeros to ensure its length is a multiple of 512 bits. The final 64 bits of this padded message store the length of the original message in bits. For instance, if the input message is 600 bits, the padded version will extend to 1024 bits, with the last 64 bits reflecting the value 600.

2. Message Parsing

   The padded message is segmented into 512-bit blocks, with each block processed sequentially through a series of rounds.

3. Message Expansion

   Each 512-bit block is expanded into 64 segments of 32 bits using a specific message expansion function, involving logical and modular arithmetic operations.

4. Compression

   The 64 segments undergo processing through a compression function, which employs logical, bitwise, and modular arithmetic operations to produce a 256-bit hash value. This compression phase consists of 64 rounds, each generating a new 32-bit segment.

5. Output Formatting

   The final hash value is formatted as a 256-bit string, which can be represented in various formats, including hexadecimal or binary.

6. Final Hash Value

   The concluding hash value is a unique 256-bit string that succinctly represents the original input message.