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Security Dictionary
Can't tell 'smtp' from 'snmp'? Find the precise meaning of these and hundreds of other security-related terms in our convenient and up-to-date Security Dictionary.
digital signature
(I) A value computed with a cryptographic algorithm and appended to a data object in such a way that any recipient of the data can use the signature to verify the data's origin and integrity. (See: data origin authentication service, data integrity service, digitized signature, electronic signature, signer.)

(I) "Data appended to, or a cryptographic transformation of, a data unit that allows a recipient of the data unit to prove the source and integrity of the data unit and protect against forgery, e.g. by the recipient." [I7498 Part 2]

(C) Typically, the data object is first input to a hash function, and then the hash result is cryptographically transformed using a private key of the signer. The final resulting value is called the digital signature of the data object. The signature value is a protected checksum, because the properties of a cryptographic hash ensure that if the data object is changed, the digital signature will no longer match it. The digital signature is unforgeable because one cannot be certain of correctly creating or changing the signature without knowing the private key of the supposed signer.

(C) Some digital signature schemes use a asymmetric encryption algorithm (e.g., see: RSA) to transform the hash result. Thus, when Alice needs to sign a message to send to Bob, she can use her private key to encrypt the hash result. Bob receives both the message and the digital signature. Bob can use Alice's public key to decrypt the signature, and then compare the plaintext result to the hash result that he computes by hashing the message himself. If the values are equal, Bob accepts the message because he is certain that it is from Alice and has arrived unchanged. If the values are not equal, Bob rejects the message because either the message or the signature was altered in transit.

(C) Other digital signature schemes (e.g., see: DSS) transform the hash result with an algorithm (e.g., see: DSA, El Gamal) that cannot be directly used to encrypt data. Such a scheme creates a signature value from the hash and provides a way to verify the signature value, but does not provide a way to recover the hash result from the signature value. In some countries, such a scheme may improve exportability and avoid other legal constraints on usage.

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