SHA-2

As explained in Real-World Cryptography

SHA-2 is a standardized family of cryptographic hash algorithms producing digests of 224, 256, 384, or 512 bits.

SHA-2 is a widely adopted family of cryptographic hash algorithms. Its variants produce 224-, 256-, 384-, or 512-bit digests; SHA-256 is common, while SHA-512 suits more cautious choices. section 2.5.1

The family includes these digest choices:

• SHA-224, SHA-256, SHA-384, and SHA-512 produce their named output lengths. section 2.5.1
• SHA-512/224 and SHA-512/256 truncate SHA-512 to 224 and 256 bits. section 2.5.1
• Internally, SHA-2 uses compression functions within the Merkle–Damgård construction: pad the message, split it into blocks, and process each block iteratively. section 2.5.1

Hashing “hello world” with OpenSSL

Run `echo -n "hello world" | openssl dgst -sha256` to produce a 256-bit digest. Switching to `-sha224`, `-sha384`, or `-sha512` changes both the digest length and the resulting value. section 2.5.1

Figure 2.6 SHA-2 and SHA-3, the two most widely adopted hash functions. SHA-2 is based on the Merkle–Damgård construction, while SHA-3 is based on the sponge construction.

Compare SHA-2’s Merkle–Damgård construction with SHA-3’s sponge construction. section 2.5

How Real-World Cryptography covers it

How deep it goes

Defines variants and sketches compression and Merkle–Damgård processing, stopping short of implementation-level detail.

Examples

Demonstrates SHA-224, SHA-256, SHA-384, and SHA-512 outputs for “hello world” using OpenSSL.

What it assumes

Assumes basic hash-function familiarity and teaches XOR before describing SHA-2’s simplified construction.

What you can do after

Operate SHA-2 variants through the OpenSSL command-line interface and distinguish their digest lengths.

How it connects

Connects SHA-2 to compression functions, XOR, Merkle–Damgård construction, SHA-3, and length-extension attacks.

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Also explained in

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  Software Security for DevelopersSHA-2 is a family of standardized cryptographic hash functions that includes SHA-224, SHA-256, SHA-384, and SHA-512.

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Related concepts

• SHA-256includes · SHA-256 is a standardized cryptographic hash function in the SHA-2 family that maps arbitrary input data to a fixed-length 256-bit digest.
• hash functionkind of · A hash function deterministically maps input data to a value in a bounded output range, commonly for indexing, lookup, comparison, or integrity checking.
• Davies–Meyer methoduses · The Davies–Meyer method is a compression-function construction that combines a block-cipher operation with a chaining value.
• Merkle–Damgård constructionkind of · The Merkle–Damgård construction builds an arbitrary-length hash function by iteratively applying a fixed-size compression function to padded message blocks.
• cryptographic hashkind of · A cryptographic hash is a fixed-length digest computed from input data by a deterministic function designed to resist preimage, second-preimage, and collision attacks.

This explainer was generated by Manning's knowledge graph from the text of Real-World Cryptography. The section links point to the parts of the book it draws on.