=== CVE-2026-5479 Reproduction Test ===
Testing EVP ChaCha20-Poly1305 tag verification

Encryption succeeded.
Ciphertext: 3d3419f9407fd11946511c5ddc637932769e4760a4c49105361ada5e4c9c9f0a
Tag:        83f993511a9ec29118243aaaad3fc58c

--- Test 1: Zeroed tag ---
EVP_DecryptUpdate ret=1, EVP_DecryptFinal_ex ret=0
Decrypted:  54686520717569636b2062726f776e20666f78206a756d7073206f7665720000
Plaintext match: YES
VULNERABLE: NO (Final rejected forged tag)

--- Test 2: Random bad tag ---
EVP_DecryptUpdate ret=1, EVP_DecryptFinal_ex ret=0
Decrypted:  54686520717569636b2062726f776e20666f78206a756d7073206f7665720000
Plaintext match: YES
VULNERABLE: NO (Final rejected forged tag)

--- Test 3: Flipped ciphertext byte + correct tag ---
EVP_DecryptUpdate ret=1, EVP_DecryptFinal_ex ret=0
Decrypted:  ab686520717569636b2062726f776e20666f78206a756d7073206f7665720000
Plaintext match: NO
VULNERABLE: NO (Final rejected modified ciphertext)