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Security Overview
Cryptography functions
Secret key (e.g., DES)
Public key (e.g., RSA)
Message digest (e.g., MD5)
Security services
Privacy: preventing unauthorized release of information
Authentication: verifying identity of the remote participant
Integrity: making sure message has not been altered Security
Cryptographyalgorithms
Publickey (e.g., RSA)
Secretkey (e.g., DES)
Messagedigest (e.g., MD5)
Securityservices
Privacy Authentication Messageintegrity
Secret Key (DES)
Plaintext
Encrypt with secret key Ciphertext
Plaintext
Decrypt with secret key
Public Key (RSA)
Encryption & Decryption
c = memod n
m = cdmod n
Plaintext
Encrypt with public key Ciphertext
Plaintext
Decrypt with private key
Message Digest
Cryptographic checksum
just as a regular checksum protects the receiver from accidental changes to the message, a cryptographic checksum protects the receiver from malicious changes to the message. One-way function
given a cryptographic checksum for a message, it is virtually impossible to figure out what message produced that checksum; it is not computationally feasible to find two messages that hash to the same cryptographic checksum. Relevance
if you are given a checksum for a message and you are able to compute exactly the same checksum for that message, then it is highly likely this message produced the checksum you were given.
