Symmetric Key Algorithms Part 2

Due to the length and the details that need to be covered I divided the Symmetric Key Algorithm section into 3 parts.

The part 1 covers the Data Encryption Standards (DES) algorithm.

This part covers 3DES, Blowfish, and IDEA.

The part 3 covers the RCA Algorithms and the ASE.


Triple DES is a symmetric key algorithms with block cipher are applied three times to each data block. The key size is increased in Triple DES to ensure additional security through encryption capabilities. Each block contains 64 bits of data. Three keys are referred to as bundle keys with 56 bits per key. There are three keying options in data encryption standards:

  1. All keys being independent
  1. Key 1 and key 2 being independent keys
  1. All three keys being identical

Key option #3 is known as triple DES. The triple DES key length contains 168 bits but the key security falls to 112 bits or 168 bits.

Triple DES is advantageous because it has a significantly sized key length, which is longer than most key lengths affiliated with other encryption modes. However, the DES algorithm was replaced by the Advanced Encryption Standard by the National Institute of Standards and Technology (NIST). Thus, the Triple DES is now considered to be obsolete.



Blowfish is a symmetric key block chipher algorithm developed in 1993. This was used in several products. There was not cryptanalysis is available for Blowfish. Blowfish is designed as an alternative for again DES and free or issue that are associated with DES.


Blowfish has a 64 bits block and a variable key lengths of 32 bits to 448 bits. It is a 16 rounds Feistle cipher.


Weakness for Blowfish is it’s susceptible to attacks on reflectively weak keys. There are advanced algorithms like Twofish or Threefish should be used in place of Blowfish. Avoid blowfish if the size of the file is more than 4GB.


IDEA – International Data Encryption Algorithm

Originally called Improved Proposed Encryption Standard (IPES) developed in 1991 to replace DES. IDEA is a minor revision of an earlier cipher, Proposed Encryption Standard (PES).

IDEA was used in Pretty Good Privacy (PGP) v2.0, and was incorporated after the original cipher used in v1.0, BassOmatic, was found to be insecure. IDEA is an optional algorithm in the OpenPGP standard.

IDEA operates on 64-bit blocks, uses 128-bit key, and consists of a series of eight identical transformations (a round) and an output transformation (the half-round). IDEA derives much of its security by interleaving operations from different groups — modular addition and multiplication, and bitwise eXclusive OR (XOR).  The process of encryption and decryption is similar.

The very simple key schedule makes IDEA subject to a class of weak keys; some keys containing a large number of 0 bits produce weak encryption.Larger classes of weak keys were found in 2002.

In 2012, full 8.5 round IDEA was finally broken, using a narrow-bicliques attack, with a reduction of cryptographic strength of about two bits, similar to the effect of the previous bicliques attack on AES.