多项选择题
Which of the following statements are true？ （）
A. RC4 is a stream cipher B. Stream ciphers require padding C. AES is a block cipher D. DES and 3DES are stream ciphers E. AES is a stream cipher F. AES， DES， and 3DES can be used as HMAC algorithms
多项选择题 Whichofthefollowingstatementsaretrueregardinghashing？（）
多项选择题 WhichtwostepsdoesareceiverperformtovalidateamessageusingHMAC？（）
单项选择题 Whichofthefollowingbestdescribesahashfunction？（）
