# OpenSSL Advisory: March 6th, 2019 (BoringSSL Not Affected)

OpenSSL have published a [security advisory](https://www.openssl.org/news/secadv/20190306.txt). Here's how it affects BoringSSL:

CVE | Summary | [Severity] in OpenSSL | Impact to BoringSSL
----|---------|-----------------------|---------------------
CVE-2019-1543 | ChaCha20-Poly1305 with long nonces | Low | Not affected, issue was introduced after fork

[Severity]: https://openssl-library.org/policies/general/security-policy/index.html#issue-severity

## CVE-2019-1543

[ChaCha20-Poly1305](https://www.rfc-editor.org/rfc/rfc7539.html) takes a 96-bit (12 byte) nonce input. OpenSSL's implementation included a non-standard extension where it took a variable-length input and zero-padded it as necessary. However, it incorrectly allowed inputs up to 16 bytes and truncated long ones down to 12 bytes. This truncation means that an application using 16-byte nonces may still internally reuse nonce values, breaking the integrity of the cipher.

BoringSSL does not implement this non-standard extension and thus is unaffected. It only accepts 12-byte nonces, matching the specification.

Note: zero-padding short nonces still results in internal collisions when a single key is used with nonces of different lengths. ChaCha20-Poly1305 should only be used with the standard 12-byte nonce length.
