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Cryptography and Cryptography and Network Security Network Security Chapter 18 Chapter 18 Fifth Edition Fifth Edition by William Stallings by William Stallings Lecture slides by Lawrie Lecture slides by Lawrie Brown Brown
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Cryptography and Network Security Chapter 18

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Cryptography and Network Security Chapter 18. Fifth Edition by William Stallings Lecture slides by Lawrie Brown. Chapter 18 – Electronic Mail Security. - PowerPoint PPT Presentation
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Page 1: Cryptography and Network Security Chapter 18

Cryptography and Cryptography and Network SecurityNetwork Security

Chapter 18Chapter 18

Fifth EditionFifth Edition

by William Stallingsby William Stallings

Lecture slides by Lawrie BrownLecture slides by Lawrie Brown

Page 2: Cryptography and Network Security Chapter 18

Chapter 18 – Chapter 18 – Electronic Mail Electronic Mail SecuritySecurity

Despite the refusal of VADM Poindexter and LtCol North to Despite the refusal of VADM Poindexter and LtCol North to appear, the Board's access to other sources of appear, the Board's access to other sources of information filled much of this gap. The FBI provided information filled much of this gap. The FBI provided documents taken from the files of the National Security documents taken from the files of the National Security Advisor and relevant NSC staff members, including Advisor and relevant NSC staff members, including messages from the PROF system between VADM messages from the PROF system between VADM Poindexter and LtCol North. The PROF messages were Poindexter and LtCol North. The PROF messages were conversations by computer, written at the time events conversations by computer, written at the time events occurred and presumed by the writers to be protected occurred and presumed by the writers to be protected from disclosure. In this sense, they provide a first-hand, from disclosure. In this sense, they provide a first-hand, contemporaneous account of events.contemporaneous account of events.——The Tower Commission Report to President The Tower Commission Report to President Reagan on the Iran-Contra Affair, 1987Reagan on the Iran-Contra Affair, 1987

Page 3: Cryptography and Network Security Chapter 18

Email SecurityEmail Security

email is one of the most widely used and email is one of the most widely used and regarded network services regarded network services

currently message contents are not secure currently message contents are not secure may be inspected either in transit may be inspected either in transit or by suitably privileged users on destination or by suitably privileged users on destination

systemsystem

Page 4: Cryptography and Network Security Chapter 18

Email Security EnhancementsEmail Security Enhancements

confidentialityconfidentiality protection from disclosureprotection from disclosure

authenticationauthentication of sender of messageof sender of message

message integritymessage integrity protection from modification protection from modification

non-repudiation of originnon-repudiation of origin protection from denial by senderprotection from denial by sender

Page 5: Cryptography and Network Security Chapter 18

Pretty Good Privacy (PGP)Pretty Good Privacy (PGP)

widely used de facto secure emailwidely used de facto secure email developed by Phil Zimmermanndeveloped by Phil Zimmermann selected best available crypto algs to useselected best available crypto algs to use integrated into a single programintegrated into a single program on Unix, PC, Macintosh and other systems on Unix, PC, Macintosh and other systems originally free, now also have commercial originally free, now also have commercial

versions availableversions available

Page 6: Cryptography and Network Security Chapter 18

PGP Operation – PGP Operation – AuthenticationAuthentication

1.1. sender creates messagesender creates message2.2. make SHA-1, 160-bit hash of message make SHA-1, 160-bit hash of message 3.3. attached RSA signed hash to messageattached RSA signed hash to message4.4. receiver decrypts & recovers hash codereceiver decrypts & recovers hash code5.5. receiver verifies received message hashreceiver verifies received message hash

Page 7: Cryptography and Network Security Chapter 18

PGP Operation – PGP Operation – ConfidentialityConfidentiality

1.1. sender forms 128-bit random session keysender forms 128-bit random session key2.2. encrypts message with session keyencrypts message with session key3.3. attaches session key encrypted with RSAattaches session key encrypted with RSA4.4. receiver decrypts & recovers session keyreceiver decrypts & recovers session key5.5. session key is used to decrypt messagesession key is used to decrypt message

Page 8: Cryptography and Network Security Chapter 18

PGP Operation – Confidentiality PGP Operation – Confidentiality & Authentication & Authentication

can use both services on same messagecan use both services on same message create signature & attach to messagecreate signature & attach to message encrypt both message & signatureencrypt both message & signature attach RSA/ElGamal encrypted session keyattach RSA/ElGamal encrypted session key

Page 9: Cryptography and Network Security Chapter 18

PGP Operation – PGP Operation – CompressionCompression

by default PGP compresses message by default PGP compresses message after signing but before encryptingafter signing but before encrypting so can store uncompressed message & so can store uncompressed message &

signature for later verificationsignature for later verification uses ZIP compression algorithmuses ZIP compression algorithm

Page 10: Cryptography and Network Security Chapter 18

PGP Operation – Email PGP Operation – Email CompatibilityCompatibility

when using PGP will have binary data to send when using PGP will have binary data to send (encrypted message etc)(encrypted message etc)

however email was designed only for texthowever email was designed only for text hence PGP must encode raw binary data into hence PGP must encode raw binary data into

printable ASCII charactersprintable ASCII characters uses radix-64 algorithmuses radix-64 algorithm

maps 3 bytes to 4 printable charsmaps 3 bytes to 4 printable chars also appends a CRCalso appends a CRC

PGP also segments messages if too bigPGP also segments messages if too big

Page 11: Cryptography and Network Security Chapter 18
Page 12: Cryptography and Network Security Chapter 18

PGP Operation – SummaryPGP Operation – Summary

Page 13: Cryptography and Network Security Chapter 18

PGP Session KeysPGP Session Keys

need a session key for each messageneed a session key for each message of varying sizes: 56-bit DES, 128-bit CAST or of varying sizes: 56-bit DES, 128-bit CAST or

IDEA, 168-bit Triple-DESIDEA, 168-bit Triple-DES generated using ANSI X12.17 modegenerated using ANSI X12.17 mode uses random inputs taken from previous uses random inputs taken from previous

uses and from keystroke timing of useruses and from keystroke timing of user

Page 14: Cryptography and Network Security Chapter 18

PGP Public & Private KeysPGP Public & Private Keys

since many public/private keys may be in use, since many public/private keys may be in use, need to identify which is actually used to encrypt need to identify which is actually used to encrypt session key in a messagesession key in a message could send full public-key with every messagecould send full public-key with every message but this is inefficientbut this is inefficient

rather use a key identifier based on keyrather use a key identifier based on key is least significant 64-bits of the keyis least significant 64-bits of the key will very likely be uniquewill very likely be unique

also use key ID in signaturesalso use key ID in signatures

Page 15: Cryptography and Network Security Chapter 18

PGP Message FormatPGP Message Format

Page 16: Cryptography and Network Security Chapter 18

PGP Key RingsPGP Key Rings

each PGP user has a pair of keyrings:each PGP user has a pair of keyrings: public-key ring contains all the public-keys of public-key ring contains all the public-keys of

other PGP users known to this user, indexed other PGP users known to this user, indexed by key IDby key ID

private-key ring contains the public/private private-key ring contains the public/private key pair(s) for this user, indexed by key ID & key pair(s) for this user, indexed by key ID & encrypted keyed from a hashed passphraseencrypted keyed from a hashed passphrase

security of private keys thus depends on security of private keys thus depends on the pass-phrase securitythe pass-phrase security

Page 17: Cryptography and Network Security Chapter 18

PGP Key RingsPGP Key Rings

Page 18: Cryptography and Network Security Chapter 18

PGP Message GenerationPGP Message Generation

Page 19: Cryptography and Network Security Chapter 18

PGP Message ReceptionPGP Message Reception

Page 20: Cryptography and Network Security Chapter 18

PGP Key ManagementPGP Key Management

rather than relying on certificate authoritiesrather than relying on certificate authorities in PGP every user is own CAin PGP every user is own CA

can sign keys for users they know directlycan sign keys for users they know directly

forms a “web of trust”forms a “web of trust” trust keys have signedtrust keys have signed can trust keys others have signed if have a chain of can trust keys others have signed if have a chain of

signatures to themsignatures to them

key ring includes trust indicatorskey ring includes trust indicators users can also revoke their keysusers can also revoke their keys

Page 21: Cryptography and Network Security Chapter 18

PGP Trust Model ExamplePGP Trust Model Example

Page 22: Cryptography and Network Security Chapter 18

S/MIME (Secure/Multipurpose S/MIME (Secure/Multipurpose Internet Mail Extensions)Internet Mail Extensions)

security enhancement to MIME emailsecurity enhancement to MIME email original Internet RFC822 email was text onlyoriginal Internet RFC822 email was text only MIME provided support for varying content MIME provided support for varying content

types and multi-part messagestypes and multi-part messages with encoding of binary data to textual formwith encoding of binary data to textual form S/MIME added security enhancementsS/MIME added security enhancements

have S/MIME support in many mail agentshave S/MIME support in many mail agents eg MS Outlook, Mozilla, Mac Mail etceg MS Outlook, Mozilla, Mac Mail etc

Page 23: Cryptography and Network Security Chapter 18

S/MIME FunctionsS/MIME Functions

enveloped dataenveloped data encrypted content and associated keysencrypted content and associated keys

signed datasigned data encoded message + signed digestencoded message + signed digest

clear-signed dataclear-signed data cleartext message + encoded signed digestcleartext message + encoded signed digest

signed & enveloped datasigned & enveloped data nesting of signed & encrypted entitiesnesting of signed & encrypted entities

Page 24: Cryptography and Network Security Chapter 18

S/MIME Cryptographic S/MIME Cryptographic AlgorithmsAlgorithms

digital signatures: DSS & RSAdigital signatures: DSS & RSA hash functions: SHA-1 & MD5hash functions: SHA-1 & MD5 session key encryption: ElGamal & RSAsession key encryption: ElGamal & RSA message encryption: AES, Triple-DES, message encryption: AES, Triple-DES,

RC2/40 and othersRC2/40 and others MAC: HMAC with SHA-1MAC: HMAC with SHA-1 have process to decide which algs to usehave process to decide which algs to use

Page 25: Cryptography and Network Security Chapter 18

S/MIME MessagesS/MIME Messages

S/MIME secures S/MIME secures a MIME entity with a a MIME entity with a signature, encryption, or bothsignature, encryption, or both

forming a MIME wrapped PKCS objectforming a MIME wrapped PKCS object have a range of content-types:have a range of content-types:

enveloped dataenveloped data signed datasigned data clear-signed dataclear-signed data registration requestregistration request certificate only messagecertificate only message

Page 26: Cryptography and Network Security Chapter 18

S/MIME Certificate S/MIME Certificate ProcessingProcessing

S/MIME uses X.509 v3 certificatesS/MIME uses X.509 v3 certificates managed using a hybrid of a strict X.509 managed using a hybrid of a strict X.509

CA hierarchy & PGP’s web of trustCA hierarchy & PGP’s web of trust each client has a list of trusted CA’s certseach client has a list of trusted CA’s certs and own public/private key pairs & certsand own public/private key pairs & certs certificates must be signed by trusted CA’scertificates must be signed by trusted CA’s

Page 27: Cryptography and Network Security Chapter 18

Certificate AuthoritiesCertificate Authorities

have several well-known CA’shave several well-known CA’s Verisign one of most widely usedVerisign one of most widely used Verisign issues several types of Digital IDsVerisign issues several types of Digital IDs increasing levels of checks & hence trustincreasing levels of checks & hence trust

ClassClass Identity ChecksIdentity Checks UsageUsage

11 name/email checkname/email check web browsing/emailweb browsing/email

22 + enroll/addr check+ enroll/addr check email, subs, s/w email, subs, s/w validatevalidate

33 + ID documents+ ID documents e-banking/service e-banking/service accessaccess

Page 28: Cryptography and Network Security Chapter 18

S/MIME Enhanced Security S/MIME Enhanced Security ServicesServices

3 proposed enhanced security services:3 proposed enhanced security services: signed receiptssigned receipts security labelssecurity labels secure mailing listssecure mailing lists

Page 29: Cryptography and Network Security Chapter 18

Domain Keys Identified MailDomain Keys Identified Mail

a specification for cryptographically a specification for cryptographically signing email messagessigning email messages

so signing domain claims responsibilityso signing domain claims responsibility recipients / agents can verify signaturerecipients / agents can verify signature proposed Internet Standard RFC 4871proposed Internet Standard RFC 4871 has been widely adopted has been widely adopted

Page 30: Cryptography and Network Security Chapter 18

Internet Mail ArchitectureInternet Mail Architecture

Page 31: Cryptography and Network Security Chapter 18

Email ThreatsEmail Threats

see RFC 4684- see RFC 4684- Analysis of Threats Analysis of Threats Motivating DomainKeys Identified MailMotivating DomainKeys Identified Mail

describes the problem space in terms of:describes the problem space in terms of: range: low end, spammers, fraudstersrange: low end, spammers, fraudsters capabilities in terms of where submitted, capabilities in terms of where submitted,

signed, volume, routing naming etcsigned, volume, routing naming etc outside located attackersoutside located attackers

Page 32: Cryptography and Network Security Chapter 18

DKIM DKIM StrategyStrategy

transparent transparent to userto user MSA signMSA sign MDA verifyMDA verify

for for pragmatic pragmatic reasonsreasons

Page 33: Cryptography and Network Security Chapter 18

DKIM DKIM Functional Functional

FlowFlow

Page 34: Cryptography and Network Security Chapter 18

SummarySummary

have considered:have considered: secure emailsecure email PGPPGP S/MIMES/MIME domain-keys identified emaildomain-keys identified email