Digital Signature
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Digital signature Digital signature is a special signature for signing electronic correspondence Note: • Sender and receiver uses same hash function • Sender informs the receiver by his public key. • Recipient informs the sender by his public key. The digital signature process: 1. Sender generates email message. 2. Hash function convert email text into strings of digits (128 or more) and takes one of the strings and applies the private key and then will have an encrypted digital signature (called a message digest). 3. Sender attaches the digital signature to the end of the email message. 4. Sender encrypts both email text message and signature with the recipient’s public key and sends to the recipient. 5. Recipient receives the email message 6. Recipient’s decrypts entire message with Recipient private key. 7. Apply same hash function used by the sender and generates the message digest and apply decryption using sender public key. 8. Recipients checks if the decrypted signature is the same as the value generated by the hash function.
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Example 1- Sara wants to send email: Welcome MIS Students. 2- Hash Function: Wel com e M IS Stu den ts. Selects a message digest: com (second block) It does encryption using receiver public key (add 1 letter) comdpn It is called digital signature 3- It adds digital signature to the end of the message Welcome MIS Students.dpn 4- Sara encrypts the entire message using Sara private key(add 2 letters) 5- Wel come MIS Students.dpn (add 2 letters) Ygneqog oku uvxfgpv.frp Sara sends encrypted message to receiver (Hasan) Receiver (Hassan) receives the entire encrypted message. Ygneqog oku uvxfgpv.frp 6- Receive (Hassan) Applies decryption using Hassan Private key (subtract 2 letters) Welcome MIS Students. dpn 7- Hash applies Hash Function same used by sender (Sara): Wel com e M IS Stu den ts. Selects a message digest: com (second block) Receiver “Hassan” applies decryption for the digital signature using Sara (sender) public key (subtract 1 letters) Dmn com 8- Compare Hash value com with decrypted digital signature com
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Example 1- Sara wants to send email: Welcome MIS Students. 2- Hash Function: Wel com e M IS Stu den ts. Selects a message digest: com (second block) It does encryption using receiver public key (add 1 letter) comdpn It is called digital signature 3- It adds digital signature to the end of the message Welcome MIS Students.dpn 4- Sara encrypts the entire message using Sara private key(add 2 letters) 5- Wel come MIS Students.dpn (add 2 letters) Ygneqog oku uvxfgpv.frp Sara sends encrypted message to receiver (Hasan) Receiver (Hassan) receives the entire encrypted message. Ygneqog oku uvxfgpv.frp 6- Receive (Hassan) Applies decryption using Hassan Private key (subtract 2 letters) Welcome MIS Students. dpn 7- Hash applies Hash Function same used by sender (Sara): Wel com e M IS Stu den ts. Selects a message digest: com (second block) Receiver “Hassan” applies decryption for the digital signature using Sara (sender) public key (subtract 1 letters) Dmn com 8- Compare Hash value com with decrypted digital signature com
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