| 摘要 |
A method of protecting a cryptosystem from a multiple transmission attack (202, 203), comprises: a) applying to a plaintext message P to be encrypted to a protective cipher having a cipher keyk, to produce a protected message (S(K)XOR P); b) creating from the protected message and the cipher key k an encryption input message (K (S(K)XOR P); and c) encrypting the message. The invention find particular although not exclusive application within public k ey cryptosystems. The invention, when used in association with a strong standar d cipher, protects against multiple transmission attack MTA by ensuring that t he text which is encrypted differs every time a message is sent, even if identical messages are sent multiple times.
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