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Understanding encryption levels

It is a common belief that the level of security depends on the number of bits used to generate an encryption key, or that a long key gives better encryption and therefore greater security than a short key. This is not completely accurate.

Keys are actually numbers that are randomly picked and then used to encrypt information. The number of possible keys depends on the "space" available to pick from, called a key space. Many misunderstand and think that the size of this key space is rated in bits when in fact that is only partly true. If you used an algorithm for generating keys that allowed only even numbers to be used as keys, the key space would actually be only half of that for an algorithm that allowed any number, if both methods used for example 16-bit encryption.

When key pairs (a public key and a private key) are generated, two large prime numbers are randomly picked (which is a process that takes time). Since there are few prime numbers to choose from compared to integers (regular numbers), which include prime numbers, the number of bits used for public keys must be very large to match the key space used for symmetric encryption, which uses integers (any number). Key pairs are used for digital certificates, and symmetric encryption is typically used for session keys.

An encryption level therefore depends on the key space, which in turn depends on the number of bits and the algorithm used to generate the keys.

For session keys, the most powerful form of encryption available in browsers today is 128-bit encryption. When generating key pairs Opera supports as much as 3072-bit encryption, but some secure sites may not support this level of encryption. Should you encounter this problem, selecting 1024-bit encryption might help.

When rating the security level of a secure document, Opera takes into consideration the following:

  • All requests used to load the page (including images, frames, and redirects)
    • Insecure images will automatically result in a level one rating
    • Other insecure content will result in level zero
  • The size of the symmetric key
  • The server's public key size

Only documents using the most secure methods (3-DES or 128-bit C4) and public keys larger than approximately 900 bits get a level three rating.

For more information about security and privacy in Opera, please read our tutorial.

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