Chinks in the armor of public key cryptosystems
W. James Wilson · 1994
Potential weaknesses in public key cryptosystem design and use are identified with emphasis on a particular vulnerability resulting from the encryption of ordinary natural language plaintext. This weakness occurs when an insufficiently long block length is used to encrypt low entropy natural language and ordinary numeric plaintext rendered in 8-bit character sets such as ASCII or EBCDIC. A computer-assisted, semi-exhaustive chosen plaintext attack is defined and shown to defeat such systems. Several methods are suggested for thwarting such attacks by maximizing input plaintext entropy prior to encryption. Keywords Public key cryptosystems, block ciphers, message entropy, unicity distance, exhaustive enumeration, n-grams, ASCII and EBCDIC character sets. 1 Introduction Although substantial information has not yet emerged in the open literature on general attack strategies against public key (PK) cryptosystems -- and by implication, steps to be taken in their defense -- the outline of c...