Reject zero-length AEAD authentication tags - #58
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GCM, EAX, CCM, ChaCha20-Poly1305, and XChaCha20-Poly1305 accepted a zero tag size through EncryptAndAuthenticate, DecryptAndVerify, and the authenticated filters, and verification with a zero-length tag reported tampered ciphertext as authentic. Reject zero in AuthenticatedSymmetricCipherBase::TruncatedFinal, which all five algorithms and both filter paths reach during finalisation. Add rejection tests for each algorithm and the GCM filters, a one-byte truncation control, and a full-tag tamper control. Reported upstream as weidai11/cryptopp issue 1364.
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AEAD APIs accepted zero-length authentication tags.
EncryptAndAuthenticateproduced no tag, whileDecryptAndVerifycould report tampered ciphertext as authentic.This affected GCM, EAX, CCM, ChaCha20-Poly1305, and XChaCha20-Poly1305 through both the one-shot APIs and authenticated filters. Reported upstream as weidai11/cryptopp#1364.
What changed
AuthenticatedSymmetricCipherBase::TruncatedFinal.The one-shot APIs process the message before finalisation, so output buffers may already contain ciphertext or unauthenticated plaintext when the exception is thrown. Callers must discard that output.
Defaults are unchanged. A filter
truncatedDigestSizeof-1still selects the full tag.