Abstract: A method of validating an encrypted message comprises:

Abstract: Parallel modulo arithmetic calculations are carried out on a device adapted to perform bitwise logical operations by storing the numbers to be operated upon in a vector form, and performing arithmetical operations on multiple numbers in parallel. The invention finds particular application in cryptosystems, as well as in other fields.

Abstract: A method of decrypting a cipher polynomial (e) using a private key (f) comprises:

Abstract: A method of protecting a cryptosystem from a multiple transmission attack, comprises:

Abstract: A method of identifying the end of a digital message, for example within a cryptosystem, uses a conversion function to convert a first string which includes the message into a second string. The first string is of a different base from the second, and the bases are chosen so that the entirety of the available space in the second string is not made use of by the conversion function. An end of message marker, which defines the position of the end element of the message within the first string, is chosen from that portion of the available space which is inaccessible to the conversion function, and the marker is then appended to the second string. The entire string may then be encrypted and sent to a recipient. The recipient uses an inverse function to locate the end of message marker and, from that, the position of the end element of the message.