Cryptographic Systems

Cryptographic Systems

1. Secure Communications Requires

2. History of Cryptography

   • Scytale
   • Caesar Cipher
   • Vigenere Cipher

3. Cipher Text

4. Crypytanalysis

5. Cryptology

   • Is the science of making and breaking secret codes
   • Cryiptology in Network

6. Cryptographic Hashes

   • A hash function takes binary data (message), and produces a condensed representation, called a hash. – The hash is also commonly called a Hash value, Message digest, or Digital fingerprint.
   • Hashes are used...To provide proof of authenticity when it is used with a symmetric secret authentication key, such as IP Security (IPsec) or routing protocol authentication

7. Hashing for integrity

8. Key Management

   • Key Generation: – Caesar to choose the key of his cipher and the Sender/Receiver chose a shared secret key for the Vigenère cipher. – Modern cryptographic system key generation is usually automated.
   • Key Verification: – Almost all cryptographic algorithms have some weak keys that should not be used (e.g., Caesar cipher ROT 0 or ROT 25). – With the help of key verification procedures, these keys can be regenerated if they occur.
   • Key Storage: – Modern cryptographic system store keys in memory.

9. Encryption = Confidentiality

10. Public Key Cryptography

    • Public-key algorithms are asymmetric algorithms based on the use of two different keys instead of one. – Private key: This key must be know only by its owner. – Public key: This key is known to everyone (it is public).
    • The key that is used for encryption is different from the key that is used for decryption. – However, the decryption key cannot, in any reasonable amount of time, be calculated from the encryption key and vice versa
    • Public-key systems have a clear advantage over symmetric algorithms: – There is no need to agree on a common key for both the sender and the receiver.

11. Digital Signatures

    • Digital signatures are often used in the following situations: – To provide a unique proof of data source, which can only be generated by a single party, such as contract signing in e-commerce environments. – To authenticate a user by using the private key of that user and the signature it generates. – To prove the authenticity and integrity of PKI certificates. – To provide nonrepudiation using a secure timestamp and a trusted time source. • Each party has a unique, secret signature key, which is not shared with any other party, making nonrepudiation possible

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