CVE-2023-1732: Improper random reading in CIRCL

When sampling randomness for a shared secret, the implementation of Kyber and FrodoKEM, does not check whether crypto/rand.Read() returns an error. In rare deployment cases (error thrown by the Read() function), this could lead to a predictable shared secret.

The tkn20 and blindrsa components does not check whether enough randomness was returned from the user provided randomness source. Typically the user provides crypto/rand.Reader, which in the vast majority of cases will always return the right number random bytes. In the cases where it does not, or the user provides a source that does not, the blinding for blindrsa is weak and integrity of the plaintext is not ensured in tkn20.