feat: add TEA and XTEA block ciphers

[thomasxm]

Summary

Adds TEA and XTEA block cipher operations to CyberChef:

• TEA (Tiny Encryption Algorithm) — Wheeler & Needham, 1994
• XTEA (eXtended TEA) — Wheeler & Needham, 1997

Both are lightweight 64-bit block ciphers with 128-bit keys, widely encountered in malware analysis and CTF challenges.

New Operations

TEA

• TEA Encrypt — Block encryption with fixed 32 cycles
• TEA Decrypt — Block decryption with fixed 32 cycles
• DELTA constant: 0x9E3779B9 (derived from the golden ratio)

XTEA

• XTEA Encrypt — Block encryption with configurable rounds
• XTEA Decrypt — Block decryption with configurable rounds
• Improved key schedule using sum-dependent key word selection
• Configurable rounds: 1–255 (default 32), matching the reference implementation by Wheeler & Needham

Common Features

• Block size: 64 bits (8 bytes)
• Key size: 128 bits (16 bytes)
• Byte order: Big-endian (matching Go stdlib, Bouncy Castle, Ironclad)
• Modes: ECB, CBC, CFB, OFB, CTR
• Padding: PKCS5, NO, ZERO, RANDOM, BIT (ISO/IEC 7816-4)

Use Cases

• Malware analysis (TEA/XTEA frequently used in malware for payload encryption)
• CTF challenges
• Embedded systems and IoT firmware analysis
• Legacy protocol decryption
• Educational purposes (studying Feistel cipher design)

Files Changed

File	Action
src/core/lib/TEA.mjs	NEW — Core TEA/XTEA library
src/core/operations/TEAEncrypt.mjs	NEW
src/core/operations/TEADecrypt.mjs	NEW
src/core/operations/XTEAEncrypt.mjs	NEW
src/core/operations/XTEADecrypt.mjs	NEW
src/core/config/Categories.json	Added 4 operations
tests/operations/tests/TEA.mjs	NEW — 28 test cases
tests/operations/index.mjs	Registered tests

Testing

• 28 test cases covering TEA and XTEA
• Test vectors sourced from Go stdlib crypto/xtea (big-endian) and Ironclad
• Round-trip encrypt/decrypt verification for all modes (ECB, CBC, CFB, OFB, CTR)
• Non-default round count tests for XTEA (16 rounds vs 32 rounds)
• All 1839 existing tests continue to pass (no regressions)

Implementation Notes

• Pure JavaScript, no external dependencies
• XTEA rounds parameter follows the same convention as RC6 (Rounds after Padding in the argument list)
• Consistent API with existing CyberChef cipher operations (RC6, SM4, Blowfish, etc.)
• TEA uses fixed 32 cycles as specified in the original paper (no configurable rounds, by design)

References

• TEA (Wikipedia)
• XTEA (Wikipedia)
• Wheeler & Needham, "TEA, a Tiny Encryption Algorithm" (1994)
• Wheeler & Needham, "Tea Extensions" (1997)
• Go stdlib crypto/xtea test vectors