Introduction To SSH [Secure SHell for VoIP]

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This is intended to be an introduction to SSH [Secure SHell], not an indepth analysis of the topic. The example of SSH is in a VoIP [Voice over Internet Protocol]. However, SSH can be used in all kinds of IP situations. One of the key points of SSH is that the connection is established and encrypted (passwords are not passed between devices in plain text) before a user is possible. SSH keys are asymmetric or symmetric. Symmetric keys are used for the session and same (symmetric) key is used to encrypt and decrypt. That is, symmetric keys are derived (created) from one another. Asymmetric uses pairs of Public and Private Keys. Rules are:

• If you encrypt with the private key, it can only be DEcrypted with the public key.

• If you encrypt with the public key, it can only be DEcrypted with the private key.

SSH uses common hash values.

For more information, check out openssh.org.

Here are a few words on “keys.”

• Public key - uses a key (means of “scrambling” or encryption) from a public source but still has its own “grooves” or codes to scramble the content or message. There are many types of encryption such as PGP [Pretty Good Privacy] which has 2 to the 1024 (two followed by 24 zeroes) power “grooves” or key combinations, 56-bit, single-key DES encryption, or others that support the much stronger 168-bit, three-key Triple DES [Data Encryption Standard] - AES [Advanced Encryption Standard] (tunnel) to encrypt files.

• Private Key - create your own “skeleton” key which no else knows about.

In addition to SSL, RSA [Rivest-Shamir-Aldeman] and other encryption algorithms, digital certificates are another means of security. However, given the real-time nature of voice and other multimedia systems, practical methods (cell phones) are also recommended if security is not possible or uncertain.

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