Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Conventional and Digital Signature: ComparisonSlide 30Slide 31Slide 32Slide 33Slide 34Slide 35Slide 36Slide 37Slide 38Slide 39Slide 40Entity Authentication: Kinds of WitnessesPasswordFixed password: AttacksOne-time passwordSlide 45Slide 46Slide 47Slide 48Slide 49Slide 50Slide 51Slide 52Slide 53Slide 54Slide 55Slide 56Slide 57Slide 58Slide 59Slide 60Slide 61Slide 62Slide 6331.1Chapter 31Network SecurityCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.31.231-1 SECURITY SERVICES31-1 SECURITY SERVICESNetwork security can provide five services. Four of these Network security can provide five services. Four of these services are related to the message exchanged using the services are related to the message exchanged using the network. The fifth service provides entity authentication network. The fifth service provides entity authentication or identification.or identification.Message ConfidentialityMessage IntegrityMessage AuthenticationMessage NonrepudiationEntity AuthenticationTopics discussed in this section:Topics discussed in this section:31.3Figure 31.1 Security services related to the message or entity31.431-2 MESSAGE CONFIDENTIALITY31-2 MESSAGE CONFIDENTIALITYThe concept of how to achieve message confidentiality The concept of how to achieve message confidentiality or privacy has not changed for thousands of years. or privacy has not changed for thousands of years. The message must be encrypted at the sender site and The message must be encrypted at the sender site and decrypted at the receiver site. This can be done using decrypted at the receiver site. This can be done using either symmetric-key cryptography or asymmetric-key either symmetric-key cryptography or asymmetric-key cryptography. cryptography. Confidentiality with Symmetric-Key CryptographyConfidentiality with Asymmetric-Key CryptographyTopics discussed in this section:Topics discussed in this section:30.5Figure 30.1 Cryptography components30.6Figure 30.2 Categories of cryptography30.7Figure 30.3 Symmetric-key cryptography30.8In symmetric-key cryptography, the same key is used by the sender(for encryption) and the receiver (for decryption).The key is shared.Note30.9Figure 30.4 Asymmetric-key cryptography30.10Figure 30.5 Keys used in cryptography30.11Figure 30.6 Comparison between two categories of cryptography31.12Figure 31.2 Message confidentiality using symmetric keys in two directions31.13Figure 31.3 Message confidentiality using asymmetric keys31.1431-3 MESSAGE INTEGRITY31-3 MESSAGE INTEGRITYEncryption and decryption provide secrecy, or Encryption and decryption provide secrecy, or confidentiality, but not integrity. However, on occasion confidentiality, but not integrity. However, on occasion we may not even need secrecy, but instead must have we may not even need secrecy, but instead must have integrity. integrity. Document and FingerprintMessage and Message DigestCreating and Checking the DigestHash Function CriteriaHash Algorithms: SHA-1Topics discussed in this section:Topics discussed in this section:31.15To preserve the integrity of a document,both the document and the fingerprint are needed.Note31.16Figure 31.4 Message and message digest31.17The message digest needs to be kept secret.Note31.18Figure 31.5 Checking integrity31.19Figure 31.6 Criteria of a hash function31.20Can we use a conventional lossless compression method as a hashing function?SolutionWe cannot. A lossless compression method creates a compressed message that is reversible. You can uncompress the compressed message to get the original one.Example 31.131.21Can we use a checksum method as a hashing function?SolutionWe can. A checksum function is not reversible; it meets the first criterion. However, it does not meet the other criteria.Example 31.231.22Figure 31.7 Message digest creation31.23SHA-1 hash algorithms create an N-bit message digest out of a message of 512-bit blocks.SHA-1 has a message digest of 160 bits (5 words of 32 bits).Note31.24Figure 31.8 Processing of one block in SHA-131.2531-4 MESSAGE AUTHENTICATION31-4 MESSAGE AUTHENTICATIONA hash function per se cannot provide authentication. A hash function per se cannot provide authentication. The digest created by a hash function can detect any The digest created by a hash function can detect any modification in the message, but not authentication. modification in the message, but not authentication. MAC (message authentication code)Topics discussed in this section:Topics discussed in this section:31.26Figure 31.9 MAC, created by Alice and checked by Bob31.27Figure 31.10 HMAC31.2831-5 DIGITAL SIGNATURE31-5 DIGITAL SIGNATUREWhen Alice sends a message to Bob, Bob needs to When Alice sends a message to Bob, Bob needs to check the authenticity of the sender; he needs to be check the authenticity of the sender; he needs to be sure that the message comes from Alice and not Eve. sure that the message comes from Alice and not Eve. Bob can ask Alice to sign the message electronically. Bob can ask Alice to sign the message electronically. In other words, an electronic signature can prove the In other words, an electronic signature can prove the authenticity of Alice as the sender of the message. We authenticity of Alice as the sender of the message. We refer to this type of signature as a digital signature.refer to this type of signature as a digital signature.ComparisonNeed for KeysProcessTopics discussed in this section:Topics discussed in this section:Conventional and Digital Signature: Comparison31.2931.30A digital signature needs a public-key system.Note31.31Figure 31.11 Signing the message itself in digital signature31.32In a cryptosystem, we use the private and public keys of the receiver;in digital signature, we use the private and public keys of the sender.Note31.33Figure 31.12 Signing the digest in a digital signature31.34Digital signature provides three out of the five services we mentioned for security systemsIntegrityAuthenticationNonrepudiation31.35A digital signature today provides message integrity.Note31.36Digital signature provides message