7)Bob uses the secret key to decrypt property description, Alice's signature and her certificate
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8)Bob decrypts Alice's digital signature with her public key which he gets from her certificate. This recovers message digest (which is 160 bit) of property description
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9)Bob uses same hash algorithm as Alice on her property description. He produces a new message digest of the decrypted property description
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10)Bob compares his calculated with transmitted message digest
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If they are exactly the same, then the material was not altered in transit and indeed came from Alice!
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If they are not the same, notify authorities
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