The Algorithms page is used to specify which algorithm(s) to use for encryption. When decrypting, CryptoForge automatically uses the correct algorithm(s).
The Speed button performs a speed test on the ciphers. Performance is evaluated using randomly-generated data in RAM memory, with no disk access or compression. The result is the average number of megabytes per second between encryption and decryption.
The speed test is intended only for comparison purposes. The actual speed of a complete encryption or decryption operation depends on a variety of factors.
For details on encryption algorithms and cryptographic security, see Security and Encryption Algorithms.
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Even though CryptoForge supports multiple encryption (encrypting with more than one algorithm at the same time), for most users any single algorithm provides a high enough level of security.