The Go package github.com/flynn/noise
, a Noise Protocol implementation, has two bugs in nonce handling in versions prior to v1.0.0.
If 2<sup>64</sup> (~18.4 quintillion) or more messages are encrypted with Encrypt
after handshaking, the nonce counter will wrap around, causing multiple messages to be encrypted with the same key and nonce, resulting in a potentially catastrophic weakening of the security properties of the symmetric cipher.
This has been resolved in the patched version by returning ErrMaxNonce
from the CipherState
Encrypt
and Decrypt
methods before the reserved maximum nonce is reached. If this error is encountered, the program should handshake again to start with a fresh CipherState
.
If an attacker sends an invalid ciphertext into one peer's Decrypt
, the nonce is incremented unconditionally. This causes a desync of the CipherState
due to a nonce mismatch between the peers, resulting in a failure to decrypt all subsequent messages. A new handshake will be required to establish a new CipherState
.
This has been resolved in the patched version by returning authentication errors from Decrypt
before incrementing the nonce.
Fixed in https://github.com/flynn/noise/pull/44, tagged as v1.0.0.
These issues were discovered during an audit of a user of this package (dnstt). Thanks to UC Berkley for commissioning the audit, and to David Fifield and Nathan Brown for their collaboration on the fixes. The fixed issues are noted in the audit as:
{ "nvd_published_at": null, "cwe_ids": [], "severity": "MODERATE", "github_reviewed": true, "github_reviewed_at": "2021-05-18T21:46:19Z" }