Improper Handling of Exceptional Conditions

Summary

In the package github.com/cloudflare/circl prior to 1.3.3, when sampling randomness for a shared secret, the implementation of Kyber and FrodoKEM, did 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 did 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".