Final answer:
RC4 is a stream cipher that supports key sizes from 8 bits to 2048 bits, with 128-bit keys being most common.
Step-by-step explanation:
The RC4 encryption algorithm supports a wide range of key sizes, specifically variable-sized key lengths from 1 byte (8 bits) to 256 bytes (2048 bits). Historically, the most commonly used key sizes are 128-bit, which provides a good balance between security and performance.
However, security experts can choose a key size that suits the level of security needed for a particular application, with larger keys providing stronger encryption but requiring more processing power to encrypt and decrypt.