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This Concept Map, created with IHMC CmapTools, has information related to: ch7 secu digi, Digital signatures: need to make sure a doc is Authentic, unforgeable, non repudiable digital signing: an electronic document or message can be signed by a principal by encrypting a copy of the message with a key and attaching it to a plaintext copy digest fucntions: called secure hash functions includes digital signatures with secret keys-MACs: problems to keep keys disclosed 1 the signer must arrange for the verifier to secretly recieve the secret key 2 may have to verify a signature in several contexts and at different times 3 the disclosure of a secret key used for signing is undesirable because a signature could be forged, Digital signatures: need to make sure a doc is Authentic, unforgeable, non repudiable digital signing: an electronic document or message can be signed by a principal by encrypting a copy of the message with a key and attaching it to a plaintext copy digest fucntions: called secure hash functions includes digital signatures with public keys: 1 generates a key pair and publishes the public key 2 computes te digest of the message using an agreed secure hash function and encrypts it using the private key to produce a signature 3 sends the signed message 4 decrypts it using published key and computes the digest of message, if they match the signature is valid, Digital signatures: need to make sure a doc is Authentic, unforgeable, non repudiable digital signing: an electronic document or message can be signed by a principal by encrypting a copy of the message with a key and attaching it to a plaintext copy digest fucntions: called secure hash functions includes secure digest functions: h=H(M) should have these properties 1 given M, it is easy to comput h 2 given h, it is hard to comput M 3 given M, it is hard to find another message M' such that H(M) = H(M') -MD5- uses four rounds, each applying one of four non linear functions to each of sixteen 32 bit segments of a 512 bit block of source text, the result is a 128 bit digest, most efficient today -SHA 1- produces a 160 bit digest but does not offer greater security against brute force and birthday style attacks usingan encryption algorithm to make a digest: the key should be published so that the digest algorithm can be applied by anyone wishing to verify a digital signature, Digital signatures: need to make sure a doc is Authentic, unforgeable, non repudiable digital signing: an electronic document or message can be signed by a principal by encrypting a copy of the message with a key and attaching it to a plaintext copy digest fucntions: called secure hash functions includes certificate standards and certificate authorities: X.509 is the most widely used standard format for certificates, which includes a subject, issuer and period of validity 1 obtain the public key and 2 validate the signature the SPKI approach: Simple Public Key Infrastructure, a scheme for the creation and management of sets of public certificates