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3.2.14 Does RSA help detect altered documents and transmission errors?

An RSA digital signature is superior to a handwritten signature in that it attests to the contents of a message as well as to the identity of the signer. As long as a secure hash function (see Question 3.8.2) is used, there is no way to take someone's signature from one document and attach it to another, or to alter the signed message in any way. The slightest change in a signed document will cause the digital signature verification process to fail. Thus, RSA authentication allows people to check the integrity of signed documents. Of course, if a signature verification fails, it may be unclear whether there was an attempted forgery or simply a transmission error.

Denis Arnaud