What is the meaning of 128 bit key in AES

Question

I am new to encryption methods and i want to know what is the meaning of 128 bit key. Does it mean the key has 128 characters or when we convert key to the binary, and then that binary has 128 digits or cipher that created using key and plain text has 128 characters ?

Answer 1

The key is 128 (binary) bits. That's all it means.

AES supports key sizes of 128, 192, or 256 bits.

AES has a fixed block size of 128 bits, which means it en/decrypts data in chunks of 16 bytes at a time. The plaintext/cipher text can be any length of course (and is padded out to a multiple of 16 bytes).

Good crypto implementations will use a Key Derivation Function which takes a password (or keyfile, etc) of any length, and generates a key suitable for the encryption algorithm in question.