Symmetric-Key Cryptosystem

See also: Security | Cryptography | Symmetric | Cryptosystem | Public-Key Cryptosystem

A cryptosystem, or method of scrambling data, that uses a single key or password to both encrypt and decrypt a given message. This key is then shared by all parties who wish to view a given encrypted file. From “symmetric,” meaning same on both sides.

  • Vulnerabilities: This method is vulnerable because a password must be communicated via phone, fax, email, or in person and, if it is ever discovered, another communication must take place.


Use in Public-Key systems

Symmetric-Key and Public-Key Cryptosystems are often used together for added security. Many Public Key systems (such as SSL) will list a Symmetric-Key system as its method of cryptography, usually DES, RC4, or 3DES along with its core system, usually RSA.


More than one algorithm can be used to protect against a possible eventual failure in one algorithm (such as the case with DES). For instance, Twofish and AES used together would be exceedingly difficult to ever hope to decrypt. The chances of a weakness being found in one system is small but both systems is very unlikely and, therefore, security is improved.


Various symmetric algorithms:

Very Strong


Strong but key too small too protect agaisnt a very determined attacker

Very Weak

  • Vigenère
  • ROT-13 (not really a symmetric algorithm as there is no password)

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