sergeych d0d79d2f07 docs: add LegacyDigest module documentation

- New docs/LegacyDigest.md: full reference for lyng.legacy_digest,
  covering the sha1() API, input types (String / Buffer), FIPS compliance
  note, and explicit guidance on appropriate vs. inappropriate use.

- docs/ai_stdlib_reference.md: entry in section 5 so AI agents know
  LegacyDigest.sha1() exists and is intentionally named as legacy-only.

- docs/whats_new.md: release-note section alongside Complex, Decimal,
  and Matrix, with a minimal runnable example and cross-link.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

2026-04-07 19:53:01 +03:00

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Legacy Digest Functions (`lyng.legacy_digest`)

⚠️ Security warning: The functions in this module use cryptographically broken algorithms. Do not use them for passwords, digital signatures, integrity verification against adversarial tampering, or any other security-sensitive purpose. They exist solely for compatibility with legacy protocols and file formats that require specific hash values.

Import when you need to produce a SHA-1 digest for an existing protocol or format:

import lyng.legacy_digest

`LegacyDigest` Object

`sha1(data): String`

Computes the SHA-1 digest of data and returns it as a 40-character lowercase hex string.

data can be:

Type	Behaviour
`String`	Encoded as UTF-8, then hashed
`Buffer`	Raw bytes hashed directly
anything	Falls back to `toString()` then UTF-8

import lyng.legacy_digest

// String input
val h = LegacyDigest.sha1("abc")
assertEquals("a9993e364706816aba3e25717850c26c9cd0d89d", h)

// Empty string
assertEquals("da39a3ee5e6b4b0d3255bfef95601890afd80709", LegacyDigest.sha1(""))

import lyng.legacy_digest
import lyng.buffer

// Buffer input (raw bytes)
val buf = Buffer.decodeHex("616263")   // 0x61 0x62 0x63 = "abc"
assertEquals("a9993e364706816aba3e25717850c26c9cd0d89d", LegacyDigest.sha1(buf))

Implementation Notes

Pure Kotlin/KMP — no native libraries or extra dependencies.
Follows FIPS 180-4.
The output is always lowercase hex, never uppercase or binary.

When to Use

Use lyng.legacy_digest only when an external system you cannot change requires a SHA-1 value, for example:

old git-style content addresses
some OAuth 1.0 / HMAC-SHA1 signature schemes
legacy file checksums defined in published specs

For any new design choose a current hash function (SHA-256 or better) once Lyng adds a lyng.digest module.

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Legacy Digest Functions (lyng.legacy_digest)

LegacyDigest Object

sha1(data): String