Ruby: fix some cases where we assume that a CryptographicOperation is using CBC when it is not

python/ql/lib/semmle/python/concepts/CryptoAlgorithms.qll

@@ -81,6 +81,8 @@ class EncryptionAlgorithm extends MkEncryptionAlgorithm, CryptographicAlgorithm
   override string getName() { result = name }
 
   override predicate isWeak() { isWeak = true }
+
+  predicate isStreamCipher() { isStreamCipher(name) }
 }
 
 /**

python/ql/lib/semmle/python/concepts/internal/CryptoAlgorithmNames.qll

@@ -65,3 +65,8 @@ predicate isStrongPasswordHashingAlgorithm(string name) {
  * Holds if `name` corresponds to a weak password hashing algorithm.
  */
 predicate isWeakPasswordHashingAlgorithm(string name) { name = "EVPKDF" }
+
+/**
+ * Holds if `name` corresponds to a stream cipher.
+ */
+predicate isStreamCipher(string name) { name = ["CHACHA", "RC4", "ARC4", "ARCFOUR", "RABBIT"] }