Weakness in Randomness Sampling for Shared Secrets in Kyber and FrodoKEM

CVE-2023-1732 · HIGH Severity

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:N

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.

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