AEAD architecture: FAuthObj + multi-call GCM (split from PR #90 concern A)

[omonien]

AEAD architecture (PR MHumm#90 Concern A only)

Package A from the cleanup roadmap: architecture for authenticated modes, without ChaCha/Poly1305.

Donor: PR #90. GCM multi-call correctness matches PR MHumm#99 semantics (absorbed).

What changed

Area	Change
Mode object	Single FAuthObj: TAuthenticatedCipherModesBase instead of dual FGCM/FCCM
Public API	IDECAuthenticatedCipher unchanged
Protected API	EncodeGCM/DecodeGCM/EncodeCCM/DecodeCCM kept as wrappers
GCM	Multi-call: GHASH partial + CTR keystream remainder + finalize in Done
Lifecycle	Init → Encode/Decode* → Done → read tag; Done idempotent; post-Done Encode/Decode raise
CCM	Still one-shot; ExpectedTag checked in TDECCipherModes.Done
InitMode	Always free previous auth object (leak fix)

Not in this PR

• ChaCha20 / XChaCha20 / Poly1305 / cmPoly1305 / SIMD / AES-NI
• PR Basically a first implementation of the chacha20 Poly1305 algorithm MHumm/DelphiEncryptionCompendium#90’s fIsLastBlock CTR model (rejected)

Behaviour note

Call Done before reading CalculatedAuthenticationResult for multi-call GCM.

Tests (Delphi 13 Win32 Console DUnit)

• GCM 19/19, CCM 16/16, non-AEAD modes green
• Residual reds: pre-existing Keccak only

Design notes: Docs/plans/2026-07-25-aead-architecture.md

This branch lives on the fork so it can be opened against upstream MHumm/development when ready.

---

Note

High Risk
Changes core GCM/AEAD lifecycle (tag only valid after Done) and streaming crypto state; callers that read the tag or stream chunks without Done may break despite preserved public API names.

Overview
This PR refactors authenticated cipher modes around a single FAuthObj (TAuthenticatedCipherModesBase) instead of separate FGCM / FCCM, while keeping IDECAuthenticatedCipher and the protected EncodeGCM/DecodeGCM/EncodeCCM/DecodeCCM entry points as dispatch wrappers.

GCM no longer computes the tag inside each Encode/Decode. It now maintains streaming GHASH state (partial blocks, ciphertext length) and CTR keystream remainder across calls, materializes CalculatedAuthenticationTag in Done, blocks further Encode/Decode after finalize, and rejects late AAD or tag bit lengths above 128. TDECCipherModes.Done calls FAuthObj.Done before the expected-tag check; InitMode always frees the previous auth object on mode change.

The AEAD base gains a virtual Done, SetDataToAuthenticate, and documented multi-call lifecycle. Tests add multi-chunk GCM vectors, Done lifecycle cases, and fix the large 256-bit-key GCM vector tag in test data.

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[augmentcode]

🤖 Augment PR Summary

Summary: Refactors AEAD handling to use a single authenticated-mode object and adds correct multi-call (streaming) GCM finalization semantics.

Changes:

• Introduced a common AEAD base contract with a virtual Done finalization step (DECAuthenticatedCipherModesBase.pas)
• Reworked TDECCipherModes to manage one FAuthObj instead of separate GCM/CCM instances, including leak-safe mode re-initialization
• Implemented streaming GCM state (running GHASH, partial blocks, CTR keystream remainder) and tag materialization in TGCM.Done
• Made post-Done GCM Encode/Decode calls raise until re-Init
• Kept protected Encode/DecodeGCM/Encode/DecodeCCM entry points as wrappers to preserve API surface
• Updated/expanded DUnit tests to cover multi-chunk GCM, Done idempotency, and post-Done rejection
• Corrected a large GCM CAVS response tag vector

Technical Notes: Callers must call Done before reading CalculatedAuthenticationResult when using multi-call GCM streams; CCM remains effectively one-shot with tag computed during Encode/Decode.

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[omonien]

Addressed 2026-07-27 (fork cleanup pass)

Linear stack restored (A → B → C) and Cursor Bugbot / Augment findings handled:

Area	Fix
GCM AAD after Encode/Done	rejected (sGCMAADLocked)
GCM tag length > 128	EDECAuthLengthException + defensive copy
EncodeCCM / DecodeCCM	independent FAuthObj dispatch (no longer forwards through EncodeGCM)
Poly1305 + block ciphers	stream-only (BlockSize < 16)
ChaCha Poly init FBufferSize	restored to Context.BufferSize
Win32 AVX XMM	save/restore on X86ASM
AES-256 AES-NI schedule	no +240 encode key; decode at (FRounds+1)*Blocks

Tests (D13 Win32 Console): GCM 21/21, ChaCha20Poly1305 12/12, AESNI 7/7. Pre-existing Keccak reds only.