encryption algorithm

A formula used to turn ordinary data, or "plaintext," into a secret code known as "ciphertext." Each algorithm uses a string of bits known as a "key" to perform the calculations. The larger the key (the more bits), the greater the number of potential patterns can be created, thus making it harder to break the code and descramble the contents.

Most encryption algorithms use the block cipher method, which codes fixed blocks of input that are typically from 64 to 128 bits in length. Some use the stream method, which works with the continuous stream of input.

The dialog box below from the ScramDisk encryption program shows the various algorithms offered to encrypt data on your hard disk. The free, open source, legacy version of ScramDisk is available at www.samsimpson.com. The accompanying descriptions and performance comparisons from the ScramDisk documentation manual are provided because they provide a brief and clear summary of current-day secret key encryption algorithms.

The following is reproduced with permission, courtesy of Sam Simpson and Aman. See mode of operation, cryptography, security protocol, stream cipher, block cipher and algorithm.

ScramDisk Encryption

ScramDisk encrypts data on the hard disk, and this dialog box allows for the selection of the encryption algorithm. "Mouse entropy" is the amount of randomness introduced into the creation of the key. The more the mouse is moved around in a random pattern, the more randomness.

3DES
This is far better than DES; it uses three applications of the DES cipher in EDE (Encipher-Decipher-Encipher) mode with totally independent keys. Outer-CBC is used. This algorithm is thought to be very secure (major banks use it to protect valuable transactions), but it is also very, very slow.

Blowfish
Blowfish is a high security encryption alogorithm designed by Bruce Schneier, the author of Applied Cryptography and owner of the company Counterpane. It is very fast, is considered secure and is resistant to linear and differential analysis. This is my personal cipher of choice.

DES
Data Encryption Standard was designed in the early 1970s by IBM with input from NSA. It is OK, but a single key can be broken in three days by the Electronic Frontier Foundation, a poorly funded organization. This algorithm was provided for completeness.

IDEA
International Data Encryption Algorithm was produced by Xuejia Lai and James Massey. It is fairly fast, is considered secure, and it is also resistant to both linear and differential analysis. To use this for anything other than personal use, a royalty must be paid to Ascom-Systec Ltd.

Misty1
Misty1 was designed by M. Matsui of Mitsubishi. It is a reasonably fast cipher that is resistant to both linear and differential analysis. It is fairly new though, so use it with caution.

Square
Square is a very fast and reasonably secure block cipher produced by John Daemen and Vincent Rijmen. It hasn't been subject to as much peer review as Blowfish, 3DES, IDEA, etc., so it may be susceptible to attacks.

Summer
This is a proprietary stream cipher constructed by the author and is designed for speed alone. It is supplied for backward compatibility with Version 1 of ScramDisk and is not recommended for use on newly created disks. Instead, use TEA or Blowfish, which are both reasonably fast.

TEA
Tiny Encryption Algorithm is a very fast and moderately secure cipher produced by David Wheeler and Roger Needham of Cambridge Computer Laboratory. There is a known weakness in the key schedule, so it is not recommended if utmost security is required. TEA is provided in 16 and 32 round versions. The more rounds (iterations), the more secure, but slower.

 Summary
                               Block  Key
                               Size   Size  Speed**
 Type      Author              Bits   Bits   (m:s)
 3DES      Diffie & Hellman     64    168    4:05
 Blowfish  Schneier             64    256    0:55
 DES       IBM & NSA            64     56    1:42
 IDEA      Lai & Massey         64    128    1:07
 Misty1    Matsui               64    128    2:50
 Square    Daemon & Rijmen     128    128    0:39
 Summer    Aman             (stream)  128    0:46
 TEA 16    Wheeler & Needham    64    128    0:46
 TEA 32    Wheeler & Needham    64    128    1:03

 **Speed is time to copy a 50MB file from a normal
   disk to a ScramDisk on a 166 Mhz Pentium.