tailieunhanh - cryptography for developers PHẦN 8

Các câu hỏi sau đây thường gặp, đã trả lời bởi các tác giả của cuốn sách này, được thiết kế cho cả hai biện pháp sự hiểu biết của bạn về các khái niệm được trình bày trong chương này và để hỗ trợ bạn thực hiện thực cuộc sống của các khái niệm này. Để có những câu hỏi của bạn về chương này trả lời của tác giả, trình duyệt / giải pháp | Message - Authentication Code Algorithms Chapter 6 293 Frequently Asked Questions The following Frequently Asked Questions answered by the authors of this book are designed to both measure your understanding of the concepts presented in this chapter and to assist you with real-life implementation of these concepts. To have your questions about this chapter answered by the author browse to solutions and click on the Ask the Author form. Q What is a MAC function A A MAC or message authentication code function is a function that accepts a secret key and message and reduces it to a MAC tag. Q What is a MAC tag A A tag is a short string of bits that is used to prove that the secret key and message were processed together through the MAC function. Q What does that mean What does authentication mean A Being able to prove that the message and secret key were combined to produce the tag can directly imply one thing that the holder of the key produced vouches for or simply wishes to convey an unaltered original message. A forger not possessing the secret key should have no significant advantage in producing verifiable MAC tags for messages. In short the goal of a MAC function is to be able to conclude that if the MAC tag is correct the message is intact and was not modified during transit. Since only a limited number of parties typically only one or two have the secret key the ownership of the message is rather obvious. Q What standards are there A There are two NIST standards for MAC functions currently worth CMAC standard is SP 800-38B and specifies a method of turning a block cipher into a MAC HMAC standard is FIPS-198 and specifies a method of turning a hash function into a MAC. An older standard FIPS-113 specifies CBC-MAC a precursor to CMAC using DES and should be considered insecure. Q Should I use CMAC or HMAC A Both CMAC and HMAC are secure when keyed and implemented safely. CMAC is typically more efficient for very .