The document discusses symmetric-key cryptosystems, public-key cryptosystems, and their problems. It then introduces hybrid cryptosystems, which combine the efficiency of symmetric-key cryptography with the convenience of public-key cryptography. As an example, it describes how Bob could encrypt a message for Alice using a hybrid system by encrypting the message with a symmetric key and then encrypting the symmetric key with Alice's public key. Finally, it discusses how hybrid encryption is used to securely share electronic documents with multiple recipients.

1. HYBRID
CRYPTOSYSTEM
Presented By:
Deeksha Agarwal
Semester 5th
University of Allahabd

2. Introduction

3. Symmetric-Key Cryptosystem

4. Public-Key Cryptosystem

5. Problems
Symmetric
• Keys must be distributed in
secret
• If a key is compromised,
Eve (eavesdropper) can
decrypt any message
pretend to be one of the
parties
• A network requires a great
number of keys
Asymmetric
• slow (~1000 times slower
than the symmetric)
• vulnerable to chosen-
plaintext attacks

6. Hybrid Cryptosystem
• combines the convenience of a public-key
cryptosystem with the efficiency of a symmetric-key
cryptosystem.
• A hybrid cryptosystem can be constructed using any
two separate cryptosystems.

9. Example
To encrypt a message addressed to Alice, Bob does the
following:
• Obtains Alice's public key.
• Generates a fresh symmetric key.
• Encrypts the message using the symmetric key just
generated.
• Encrypt the symmetric key using Alice's public key.
• Send both of these encryptions to Alice.

10. Cont...

11. Cont...
To decrypt this hybrid ciphertext, Alice does the
following:
• uses her private key to decrypt the symmetric key
contained in the key encapsulation segment.
• uses this symmetric key to decrypt the message
contained in the data encapsulation segment.

12. Cont...

13. Hybrid Encryption in Electronic
Document
• Electronic document information suffers from
disclosed, counterfeited, tampered, repudiated and
so on.
• To solve the above problem we used hybrid
encryption technology using
encryption technology, digital digest, digital
authentication and digital signature .

14. Cont...
• Adobe Acrobat software uses hybrid approaches so
single documents can be protected for multiple
recipients, each possessing unique key pairs.
The file size is not significantly increased during
this method because the entire document does not
need to be encrypted for each person.

15. Conclusion

16. THANKYOU