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SHA-256 (Secure Hash Algorithm 256-bit) is a cryptographic hash function that belongs to the SHA-2 family. It takes an input (or 'message') and returns a fixed-size 256-bit (32-byte) hash value, typically rendered as a 64-character hexadecimal number.
The SHA-256 algorithm processes input data through multiple rounds of compression functions. It:
The input message is padded to a multiple of 512 bits using a specific padding scheme that includes the original message length.
The padded message is broken into 512-bit blocks for processing.
Eight 32-bit initial hash values are set using constants derived from the fractional parts of square roots of the first eight prime numbers.
Each 512-bit block undergoes 64 rounds of compression using logical functions, bitwise operations, and modular addition.
After processing all blocks, the eight hash values are concatenated to produce the final 256-bit hash value.
Verify that files haven't been altered during transfer or storage by comparing SHA-256 checksums.
Websites often store password hashes instead of plain text passwords for security.
Used in digital certificates and SSL/TLS to verify the authenticity of digital documents.
Cryptocurrencies like Bitcoin use SHA-256 for mining and transaction verification.
Software vendors provide SHA-256 checksums to verify downloaded files haven't been tampered with.
Digital forensics experts use SHA-256 to create unique identifiers for digital evidence.
| Hash Function | Output Size | Security Level | Common Uses |
|---|---|---|---|
| SHA-256 | 256 bits | High | Blockchain, SSL certificates, password storage |
| MD5 | 128 bits | Broken | File integrity checks (non-security) |
| SHA-1 | 160 bits | Weak | Legacy systems, Git version control |
| SHA-512 | 512 bits | Very High | High-security applications |
While MD5 and SHA-1 were once widely used, they now have known vulnerabilities that make them unsuitable for security purposes. SHA-256 provides significantly better security and is currently considered cryptographically secure for most applications.
Encryption is a two-way process that converts data into ciphertext that can be decrypted back to the original data with the correct key. Hashing is a one-way function that converts data into a fixed-length string that cannot be reversed. SHA-256 is a hash function, not an encryption algorithm.
In theory, yes - this is called a hash collision. However, with SHA-256, the probability of a collision is astronomically small (approximately 1 in 2^128). For practical purposes, SHA-256 is considered collision-resistant.
While SHA-256 is cryptographically secure, it's not ideal for password storage by itself because it's fast to compute, making it vulnerable to brute-force attacks. For password storage, it's better to use specialized algorithms like bcrypt, Argon2, or PBKDF2 which are intentionally slow and include salt.
A SHA-256 hash is always 256 bits (32 bytes) long. When represented in hexadecimal format, it appears as a 64-character string (since each hexadecimal character represents 4 bits).
No, SHA-256 is a one-way function. It's designed to be computationally infeasible to reverse the process and obtain the original input from the hash value. The only way to "decrypt" a hash is through brute-force guessing, which is impractical for strong inputs.
Some alternatives include other SHA-2 variants (SHA-384, SHA-512), SHA-3 (the latest standard), BLAKE2, and BLAKE3. For specific use cases like password hashing, bcrypt, Argon2, and scrypt are preferred.