Cryptography - The Science of Secrecy |

The following table provides a little list of some of the most common schemes employed today for a variety of functions. The Table also includes several real cryptographic applications that many of us employ (knowingly or not) everyday; for password protection and private communication.

DES (Data Encryption Standard) |
DEA is an improvement of the algorithm Lucifer (developed by IBM). The DEA has a 64-bit block size and uses a 56-bit key during execution (8 parity bits are stripped off from the full 64-bit key). The DEA is a symmetric cryptosystem. DES invokes 16 rounds of permutations, swaps, and substitutes. |

RSA |
The RSA cryptosystem is a public-key cryptosystem that offers both encryption and authentication. Created by Ron Rivest, Adi Shamir, and Leonard Adleman This is the first asymmetric key system. This is the basis of today’s Public Key Infrastructure. |

Advanced Encryption Standard (AES) |
NIST replacement of DES, using a very public process over a 4-1/2 year period. |

Blowfish |
Secret-key, block-cipher cryptosystem with widely varying key-length. Designed by Bruce Schneier, it is available freely to any user as a substitute for DES or IDEA. |

Diffie-Hellman |
In 1976 First public-key cryptosystem, used for key exchange for secret-key (symmetric) cryptosystems. |

Elliptic Curve Cryptography (ECC) |
A relatively new PKC algorithm based upon elliptic curves. ECC can offer levels of security comparable to RSA and other PKC methods with much smaller keys. It is well-suited to devices that are resource constrained, such as smartcards and PDAs. |

Pretty Good Privacy (PGP) |
A family of cryptographic routines for e-mail and file storage applications developed by Philip Zimmermann in 1991. PGP 2.6.x uses RSA for key management and digital signatures, IDEA for message encryption, and MD5 for computing the message's hash value. |

Message Digest (MD) algorithms: 2,4,5 |
Message-digest algorithms, used for digital signature applications for message integrity. |

International Data Encryption Algorithm (IDEA) |
Secret-key cryptosystem written by Xuejia Lai and James Massey, in 1992 and patented by Ascom; a 64-bit SKC block cipher using a 128-bit key. |

Public-Key Cryptography Standards (PKCS) |
A set of interoperable standards and guidelines for public-key cryptography, designed by RSA Data Security Inc. |

** **

**Cracking an algorithm**** ***(Cryptanalysis* and *Attacks*
on Cryptosystems)

*Cryptanalysis *is the flip-side of
cryptography: It is the art of deciphering encrypted communications without
knowing the proper keys. In order to design a robust encryption algorithm or
cryptographic protocol, one should use cryptanalysis to find and correct any
weaknesses. This is precisely the reason why the most trusted encryption
algorithms are ones that have been made available to public scrutiny.

The various techniques in cryptanalysis attempting to compromise cryptosystems are referred to as attacks. Some of the better-known attacks (or techniques) are as follows.

** Brute
force attack**: This attack requires trying all (or a large
fraction of all) possible values till the right value is found; also called
an exhaustive search.

** Cipher
text only attack**: This is the situation where the attacker does not know
anything about the contents of the message, and must work from cipher text
only. In practice it is quite often possible to make guesses about the plain
text contents of messages, as many types of messages have fixed-format
headers.

** Known
plain text attack**: The attacker knows or can guess the plain text for some
parts of the message. The task is to decrypt the rest of the cipher text
blocks using this information. This may be done by determining the key used
to encrypt the data, or via some shortcut.

** Chosen
plain text attack**: The attacker is able to have any text he likes encrypted
with the unknown key. The task is to determine the key used for

encryption.

** Algebraic
attack**:
A method of cryptanalytic attack used against block ciphers that exhibit a
significant amount of mathematical structure.

** Man-in-the-middle
attack**:
This attack is relevant for cryptographic communic-ation and key exchange
protocols. When two parties are exchanging keys for secure communications (

** Timing
Attack**:
This attack is based on repeatedly measuring the exact execution times of
modular exponentiation operations. It is relevant to at least RSA,
Diffie-Hellman, and Elliptic Curve methods.

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