Which key size is used in Blowfish?

Blowfish is a symmetric-key block cipher that supports a variable key length ranging from 32 bits to 448 bits. This flexibility in key size is one of the cipher's significant features, as it allows users to choose the level of security that best fits their specific needs. A longer key generally provides better security, and Blowfish's range facilitates this.

The other options do not accurately represent the capabilities of Blowfish. For instance, the first option limits the key size to a maximum of 128 bits, which is incorrect as it doesn’t encompass the full range of key lengths available in Blowfish. The second option suggests the maximum of 256 bits, which again is too restrictive since Blowfish goes up to 448 bits. Lastly, the final option incorrectly states a maximum key size of 512 bits, which exceeds the actual limit for Blowfish. Therefore, the correct answer is based on the cipher's ability to handle a variable key size within the stated range.