B2B Integration : A Practical Guide to Collaborative E-commerce

298 B2B Integration — A Practical Guide to Collaborative E-commerce
When the receiver gets the message, it performs the following
actions:
1. It decrypts the message using its private key (see Figure 10.7). Now
what it sees is the digital signature and the original message file.
2. It re-computes the 'digest' from the original file, using the same hash
algorithm.
3. It decrypts the digital signature using the sender's public key.
4. It then compares the decrypted digital signature with the digest that it
just computed.
5. If the two are exactly the same, the receiver is assured that the
message was not changed en route and also that the sender's identity
is proved (as the sender's private key was involved in the process;
see Figure 10.8).
Receiver's
Private Key
Secured Message
Received
Message
Digital
Signature
Figure 10.7. — Decryption using digital signature
Hash
Function Sender's Public
Key
Message
Digital
+ Signature
Message Message
Digest Digest
Pass/
Fail
Figure 10.8.
message
Ensuring integrity of the