Implement SHA-256 (SHA-2) cryptographic hash function

[Copilot]

Adds SHA-256 implementation to complement existing SHA-0 and SHA-1 algorithms.

Implementation

• sha256.hh/sha256.cc (410 lines): Complete SHA-256 algorithm following NIST FIPS 180-4

  • 8 state registers (h0-h7) for 256-bit digest
  • 64 compression rounds with K constants derived from cube roots of first 64 primes
  • Message schedule expansion using σ0/σ1 functions
  • Right rotate/shift operations for SHA-256 specifics

• common_hash.hh: Added cripto_test_sha256() and openssl_test_sha256() wrapper functions

• ut_sha_functions.cc: 10 unit tests covering empty strings, special characters, non-ASCII, 1M character strings, randomized inputs, determinism, and avalanche effect

• main.cc/sha_cli.cc: Integrated SHA-256 alongside SHA-1 in test harness and CLI tool

Usage

cripto::SHA256 sha256;
uint8_t digest[cripto::SHA256_DIGEST_SIZE];

sha256.initialization(reinterpret_cast<const uint8_t*>(data), length);
sha256.final(digest);

std::string hash = cripto::SHA256::toHexString(digest, cripto::SHA256_DIGEST_SIZE);
// SHA256("abc") = ba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad

Verified against standard NIST test vectors. All outputs match OpenSSL implementation.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• center2.conan.io
  • Triggering command: /usr/bin/python3 /home/REDACTED/.local/bin/conan install . --output-folder=build --build=missing (dns block)
• esm.ubuntu.com
  • Triggering command: /usr/lib/apt/methods/https (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Original prompt

Implementa SHA2

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