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Add support for constant-time decryption of PKCS#1 v1.5-encoded session keys #1445

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merged 8 commits into from Jan 19, 2022
Merged

Add support for constant-time decryption of PKCS#1 v1.5-encoded session keys #1445

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8ee1cfc
WIP
larabr Nov 17, 2021
8dd495a
Implement constant time decryption flow for RSA and ElGamal PKESK
larabr Nov 30, 2021
1fcbb48
Add constant-time select
larabr Dec 1, 2021
11a00f2
Update comments
larabr Dec 1, 2021
d3ecad0
Fix test
larabr Dec 1, 2021
9031105
Check checksum in constant time
larabr Dec 2, 2021
b96a33f
Fix typo in comment [skip ci]
larabr Dec 2, 2021
ecca368
Rename variables
larabr Dec 2, 2021
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7 changes: 4 additions & 3 deletions src/packet/public_key_encrypted_session_key.js
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Expand Up @@ -129,10 +129,11 @@ class PublicKeyEncryptedSessionKeyPacket {
util.writeChecksum(randomSessionKey.sessionKey)
]) : null;
const decoded = await crypto.publicKeyDecrypt(this.publicKeyAlgorithm, key.publicParams, key.privateParams, this.encrypted, key.getFingerprintBytes(), randomPayload);
const checksum = decoded.subarray(decoded.length - 2);
const sessionKey = decoded.subarray(1, decoded.length - 2);
const symmetricAlgoByte = decoded[0];
const isValidChecksum = util.equalsUint8Array(checksum, util.writeChecksum(sessionKey));
const sessionKey = decoded.subarray(1, decoded.length - 2);
const expectedChecksum = decoded.subarray(decoded.length - 2);
const actualChecksum = util.writeChecksum(sessionKey);
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const isValidChecksum = actualChecksum[0] === expectedChecksum[0] & actualChecksum[1] === expectedChecksum[1];

if (randomSessionKey) {
// We must not leak info about the validity of the decrypted checksum or cipher algo.
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