CONNOTECH Experts-conseils Inc.

Message salting with the Frogbit algorithm

The Frogbit cipher allows the use of a single secret key for multiple encryptions, with the following initialization procedure:

1. the secret key defines part of (or all) the initial Frogbit state (this is the same as if salting is not used), and
2. a fixed number of random bits are encrypted before the actual message encryption starts.

The required number of bits may be in the range of 16 to 64. In the field of cryptography, this is known as salting (the deliberate and unilateral addition of meaningless random bits to a message). The random bits need not be shared with the legitimate receiver of the message. They are encrypted, their ciphertext is sent to the receiver as a message prefix. The receiver simply decrypts them and ignores them.

This scheme is a significant reduction of the key management overhead for stream ciphers. The unmodified stream cipher requires a unique shared secret key for every message. The Frogbit cipher initialized with message salting needs only a private random source in the sender's computing environment (the secret key is set like in the case of a block encryption algorithm). The requirement for message salting is independent from the design flexibility of secret state initialization: it occurs whenever a single secret key is used for more than one message, and attacks on the first few bits of the message are to be prevented.

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