Abstract. RC4, a stream cipher designed by Rivest for RSA Data Security Inc., has found several commercial applications, but little public analysis has been done to date. In this paper, alleged RC4 (hereafter called RC4) is described and existing analysis outlined. The properties of RC4, and in particular its cycle structure, are discussed. Several variants of a basic "tracking" attack are described, and we provide experimental results on their success for scaled-down versions of RC4. This analysis shows that, although the full-size RC4 remains secure against known attacks, keystreams are distinguishable from randomly generated bit streams, and the RC4 key can be recovered if a significant fraction of the full cycle of keystream bits is generated (while recognizing that for a full-size system, the cycle length is too large for this to be practical). The tracking attacks discussed provide a significant improvement over the exhaustive search of the full RC4 keyspace. For example, the state of a 5 bit RC4-like cipher can be obtained from a portion of the keystream using 2 42 steps, while the nominal keyspace of the system is 2 160 . More work is necessary to improve these attacks in the case where a reduced keyspace is used.

Abstract. Key derivation functions are commonly used within many cryptographic schemes in order to distribute the entropy contained in an uneven way in a long stream of bits into a string that can be used directly as a symmetric key or as a seed for a pseudo-random number generator, or to convert short strings such as passwords into symmetric keys. This paper examines the common key derivation function constructions and shows that most of these have some concerning properties. In some situations, the use of these key derivation functions may actually limit the security that would otherwise be obtained. A new construction is also provided which seems to have better properties and an intuitive justification for its security is given.

Abstract. This paper describes an adaptive chosen-ciphertext attack on the Cipher Feedback (CFB) mode of encryption as used in OpenPGP. In most circumstances it will allow an attacker to determine 16 bits of any block of plaintext with about 2 15 oracle queries for the initial setup work and 2 15 oracle queries for each block. Standard CFB mode encryption does not appear to be affected by this attack. It applies to a particular variation of CFB used by OpenPGP. In particular it exploits an ad-hoc integrity check feature in OpenPGP which was meant as a "quick check" to determine the correctness of the decrypting symmetric key.

In this work, we assessed the impact of post-quantum (PQ) cryptography on public key infrastructure (PKI). First, we modified a commercially available certification authority (CA) to issue 'hybrid' certificates (X.509 certificates with PQ extensions). Then we assessed the impact of using these certificates on some existing protocols, including TLS, OCSP, CMP, and EST, with open-source libraries OpenSSL and CFSSL, and with a commercially available cryptographic toolkit. We found that most of the protocols and libraries we tested worked with hybrid certificates, and some of the failures could be overcome with minor modifications to the existing software. Our work differentiates from and extends previous work by focusing on the impact of PQ algorithms on certificate issuance, revocation, and management protocols, which are necessary for enterprises to manage PKI in their environments. The impact on TLS is also investigated, allowing consistency with previous results to be evaluated.

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