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chacha20: Reorder MAC verification and decryption process #254

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Merged
utelle merged 1 commit into from
Sep 3, 2026
Merged

chacha20: Reorder MAC verification and decryption process #254

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21 changes: 12 additions & 9 deletions src/cipher_chacha20.c
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Original file line number Diff line number Diff line change
Expand Up @@ -311,19 +311,16 @@ DecryptPageChaCha20Cipher(void* cipher, int page, unsigned char* data, int len,

if (nReserved > 0)
{
int allzero = 0;
/* Decrypt and verify MAC */
memset(otk, 0, OTK_LEN_CHACHA20);
counter = LOAD32_LE(data + n + PAGE_NONCE_LEN_CHACHA20 - 4) ^ page;
chacha20_xor(otk, OTK_LEN_CHACHA20, chacha20Cipher->m_key, data + n, counter);

/* Determine MAC and decrypt */
allzero = chacha20_ismemset(data, 0, n);
poly1305(data, n + PAGE_NONCE_LEN_CHACHA20, otk, tag);
chacha20_xor(data + offset, n - offset, otk + 32, data + n, counter + 1);

/* Only calculate and verify MAC if required */
if (hmacCheck != 0)
{
poly1305(data, n + PAGE_NONCE_LEN_CHACHA20, otk, tag);

/* Verify the MAC */
if (poly1305_tagcmp(data + n + PAGE_NONCE_LEN_CHACHA20, tag))
{
Expand All @@ -335,11 +332,17 @@ DecryptPageChaCha20Cipher(void* cipher, int page, unsigned char* data, int len,
SQLITE3MC_DEBUG_HEX("decrypt data+n:", data + n, 16);
SQLITE3MC_DEBUG_HEX("decrypt tag r:", data + n + PAGE_NONCE_LEN_CHACHA20, PAGE_TAG_LEN_CHACHA20);
SQLITE3MC_DEBUG_HEX("decrypt tag c:", tag, PAGE_TAG_LEN_CHACHA20);
/* Bad MAC */
rc = (page == 1) ? SQLITE_NOTADB : SQLITE_CORRUPT;

/* Bad MAC: Clean up and bail out BEFORE decrypting */
sqlite3mcSecureZeroMemory(otk, OTK_LEN_CHACHA20);
return (page == 1) ? SQLITE_NOTADB : SQLITE_CORRUPT;
}
}
if (page == 1 && usePlaintextHeader == 0 && rc == SQLITE_OK)

/* Decrypt only after MAC is verified (or if check is bypassed) */
chacha20_xor(data + offset, n - offset, otk + 32, data + n, counter + 1);

if (page == 1 && usePlaintextHeader == 0)
{
memcpy(data, SQLITE_FILE_HEADER, 16);
}
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