1. International Standards Public Key Infrastructure

2. Public key systems  Each entity has a key pair (s,p)  Confidentiality C=E(p,M) and M = D(s,C)  Authenticy Signature = S(s,M) and V(p,Signature) = accept

3. RSA Signature  RSA keys  P, Q primes  PQ=N  ed 1 (mod (P-1)(Q-1))  P, Q, d private  e, N public

4. RSA Signature example  Transform the data to be signed to a unique form: enc  MD = Hash(enc)  PAD to N –D = 00 01 FF... FF 00 MD  Sign –S = D d (mod N)  Send data and S

5. RSA Signature example  Transform the signed data to the unique form: enc  MD = Hash(enc)  Decrypt –D = S e (mod N)  Remove padding and compare MD

6. Key management  Key creation  Key distribution  Key renewal  Key revocation  Key validation control

7. Certification authorities  CA –Trusted Third Party –(s,p) –Publish public keys  Signs –Entity’s identity –Entity’s public key  Certificate

8. Certificate authorities  Cross certification  Chains

9. The life cycle of a user certificate Issue Store Use Renew Revoke Register

10. International standards  ASN.1 –Everything is build upon ASN.1  X.509  PKCS  PKIX  S/MIME  OCSP  Public Key Cryptographic Standard  #1 RSA encryption Standard  #5 Password-Based Encryption  #7 Cryptographic Message Syntax  #8 Private-Key Infomation  #10 Certification Request  #12 Personal Information Exchange Syntax

11. Abstract Syntax Notation One  ASN.1  Language to describe structured data –Everything is specified in ASN.1  Types and values –Simple –Structured

12. ASN.1 simple types  INTEGER  NULL  BOOLEAN  ENUMERATED  BIT STRING  OCTET STRING  OBJECT IDENTIFIER

13. OBJECT IDENTIFIER  Giving object name –Distinguish between different types of obejcts  Algorithms  Types (X509 Extensions og name attributes)  Object identifier tree –CCITT {0} –ISO {1} –Both {2}

14. Examples  RSA –pkcs-1 OBJECT IDENTIFIER ::= { iso(0) member-body(2) us(840) rsadsi(113549) pkcs(1) 1} –rsaEncryption OBJECT IDENTIFIER ::= { pkcs-1 1 } –sha1WithRSAEncryption ::= { pkcs-1 5 }  X.509 –Id-at OBJECT IDENTIFIER ::= {joint-iso-ccitt(2) ds(5) 4} –Id-at-commonName OBJECT IDENTIFIER ::= {id-at 3}

15. Characters and times  Characters –Printable –TeleTex –IA5 –Visible  Times –UTC –Generalized

16. Structured types  SET and SET OF  SEQUENCE and SEQUENCE OF  CHOICE  ANY –Used when there are ”holes” in the definition.  TAGS –Everything has a tag

17. TAGS  Creates new types from old types  Used to distinguish types CHOICE ::= { aInteger, bInteger } CHOICE ::= { a[0] Integer, b[1] Integer }  IMPLICIT (new tags replaces old tag)  EXPLICIT (new tag is added)  DEFAULT and OPTIONAL

18. Encoding Rules  Serialize and deserialize objects  Basic –Length of objets can be indefinite –Objects in sets are not sorted  Distinguished  (Packed and Confidential)

19. ENCODING  Identifier Length Content ILC IL ILILC ILC

20. Identifier  Class –Universal 0 0 described in the ASN.1 standard –Context-specific 1 0 not described in the ASN.1 standard  Form –Simple 0 –Structurered 1  Tag number –5 bit (11111 used for large tag numbers) -> 0..30 87654321 ClassP/CTag number

21. EXAMPLE  X.509 (EXPLICIT TAGGING) Extensions [3] SEQUENCE OF... -SEQUENCE OF is an Universal structured type with tag 16 -> Class = 00, C = 1, 16 = 10000 : 0011 0000 = 30 -Extensions [3] is a Context-Specific structured type with tag 3 -> Class = 10, C = 1, 3 = 00011 :1010 0011 = A3 A3L+2 30LC

22. LENGTH  Short 7 bit gives 127 Octets  Long (simplified) –1000 0001 = 81 –1000 0002 = 82 87654321 0LLLLLLL 8765432187654321 10000001LLLLLLLL

23. LENGTH  Indefinite 87654321 10000000 8765432187654321 0000000000000000

24. CONSTRUCTED ENCODING  Simple types can be encoded like a structured object –BITs, OCTETs, Characters Example: Octetstring ”ABCDEF0123456789” 0416ABCDEF0123456789 048ABCDEF01 2420 04823456789

25. The life cycle of a user certificate Issue Store Use Renew Revoke Register

26. User registration  Ensure entity’s indentification  Registration Office –Post Office –System administrator –Bank –...  Result –PIN code for authentification to CA –Private key and certifcate

27. The life cycle of a user certificate Issue Store Use Renew Revoke Register

28. Issueing certificates  Generate a key pair (s,p)  Prove s by signing indentity and p M = p||idSignature = S(s,M)  Send M and Signature to CA  CA verifies identity and signature  CA issues certificate

29. EXAMPLE  Certificate request CertificationRequest ::= SEQUENCE { certificationRequestInfoCertificationRequestInfo signatureAlgorithmAlgorithmIdentifier signatureBIT STRING } CertificationRequestInfo ::= SEQUENCE { versionVersion, subjectName, subjectPublicKeyInfoSubjectPublicKeyInfo, attributes[0] IMPLICIT Attributes }  Internet Explorer  No user authentication

30. PKIX  Public Key Infrastructure X.509 –Family of standards –Protocols for  issue certificate  certificate management  time stamps  status of certificates –Certificate and CRL profile –Certificate Practise Statement

31. PKIX CMP  Certificate Management Protocols –Protocol messages for  Certificate requests  Certificate renewal  Certificate revocation ... –Certificate request provides authentication  User gets secret key at registration (out-of-band)  Used to protect the certificate request –provide authentication (MAC)

32. PKIX CMP PKIMessage ::= SEQUENCE { headerPKIHeader, bodyPKIBody, protection[0] PKIProtection OPTIONAL, extraCerts[1] SEQUENCE OF Certifcate OPTIONAL} PKIHeader ::= SEQUENCE { senderGeneralName, recipientGeneralName, messageTime[0] GeneralizedTime OPTIONAL, protectionAlg[1] AlgorithmIdentifier OPTIONAL, senderKeyID[2] OCTET STRING OPTIONAL,... } Body contains the ”real” content

33. PKIX CMC Issue  Authentication –User gets secret key after registration (eg. PIN letter) –Used to protect request  Password Based MAC PKIBODY ::= CHOICE {... CERTReqMessages,... } CertReqMessage ::= SEQUNCE { CertReq CertRequest, pop ProofOfPossession OPTIONAL, regInfo Attributes OPTIONAL} CertRequest ::= SEQUENCE { certReqIdINTEGER, certTemplate CertTemplate } CertTemplate ::= SEQUENCE { Version[0] INTEGER, serialNumber [1] INTEGER, signingAlg[2] AlgorithmIdentifier, issuer[3] Name, subject[4] Name, validity[5] Validity, publickey[6] SubjectPublicKeyInfo,... extensions[9] Extensions }

34. X.509 Certificates  The most widespread on the Internet  In version 3 Extentions were added –Basically holes where you can put anything –Adds flexibility –Causes interoperability problems

35. X.509 Certificates  Certificate –Version –Serial number –Signature algorithm –Issuer –Validity –Subject –Public key –Extensions –Signature

36. X.509 Syntax Certificate ::= SEQUENCE { tbsCertificateTBSCertificate, signatureAlgorithmAlgorithmIdentifier, signatureValueBIT STRING } TBSCertificate ::= SEQUENCE { version[0] DEFAULT v1, serialNumberInteger, signatureAlgorithmIdentifier, issuerName, validityValidity, subjectName, subjectPublicKeyInfoSubjectPublicKeyInfo,.. extensions[0] Extensions OPTIONAL }

37. X.509 standard extensions  Basic Constraints –Is this a CA certificate –Chain length  Key –Usage –Extended –Private key usage period  Key Identifiers  Alternative Name  Name constraints  CRL Distribution Points  Policy –Issuers policy  Identifier –1.3.6.1.4.1.4386.2.2.2.1.1  CPS –http://www.certifikat.dk/repository  User notice –This certificate is issued under TDC Internet Cas Certificate Policy for Class II Certificates (OID=1.3.6.1.4.1.4386.2.2.2.1.1). –Constraint –Mapping

38. Certificate Policy  The entity is correct  Usage –Authenticity and confidentiality and maybee more  Publish certificate status  Registration is done properly  Entitiy –Correct authentication to LRA –Respect key usage –Protect private key –If compromised revoke certificate –Check validity before use  Receiver –Check certificate  Phone number

39. X.509 other extensions  Qualified Certificate –CA’s says that the certificate is a QC –issued by CA with a public statement –indicates a policy consistent with CA –living human entity with pseudonym or real name of subject  Biometric Information  Procuration  Admission  Monetary Limit  Majority  Certificate Status

40. The life cycle of a user certificate Issue Store Use Renew Revoke Register

41. Certificate storage  Browser  Disk  Token  Next time

42. Certificate and private key storage  Encoded X.509 –One public key  PKCS#8 –Private key  PKCS#7 –Public key –Certificate chains  PKCS#12 –Private key and chain –Authenticated by you

43. The life cycle of a user certificate Issue Store Use Renew Revoke Register Can you ?

44. Certificate usage  Encryption –Recipient certificate should be validated before use  Signature –Recipient should validate signer certificate  Certificate validation –Signature and validity –Chain –Revocation

45. Revocation  CRL –Signed list of serial numbers of all revoked certifcates for a particular CA  OCSP –Signed reply  Instant Certificates –Certificate holds their own status and time stamp –Requester gets a updated and re-signed certificate CertificateList ::= SEQUENCE { tbsCertList TBSCertList, algorithm AlgorithmIdentifier, signature BIT STRING} TBSCertList::= SEQUENCE { versionINTEGER, signature AlgorithmIdentifier, IssuerName, thisUpdateTime, nextUpdate Time OPTIONAL, revoedCertificates SEQUENCE OF Entry, crlExtensionsOPTIONAL } Entry ::= SEQUENCE { userCertificate SerialNumber, revocationDate Time, entryExtension Extensions OPTIONAL}

46. CRL extensions  CRL extension –Serial number –Delta CRL  Base number  Entry extension –Invalidity date –Reason code  0 unspecified  1 key comprimisied  2 CA comprimisied  3 affiliation changed  4 superseeded  5 cessation of operation  6 certificate on hold  8 remove from CRL  9 privilege withdrawn

47. CRL

48. The life cycle of a user certificate Issue Store Use Renew Revoke Register

49. Cryptographic Message Syntax  PKCS#7 –Behind everything  Signed data  Encrypted data  Uses certificates  Transport data –CRL and certificate  Behind S/MIMEv2 –Used by standard email clients  CMS –Extends PKCS#7  Key exchange –Previously agreed conventional key  Key agreement –DH scheme  Can use certificate  Behind S/MIMEv3

50. PKCS#7 Signed data SignedData ::= SEQUENCE { versionINTEGER, digestAlgorithmsDigestAlgorithmIdentifiers, contentInfoContentInfo, certificatesCertificates OPTIONAL, crlsCRLs OPTIONAL, signerInfosSignerInfos } SignerInfo ::= SEQUENCE { versionINTEGER, ISNIssuerAndSerialNumber, digestAlgorithmAlgorithmIdentifier, authenticatedAttributesAttributes OPTIONAL digestEncryptionAlgorithm AlgorithmIdentifier, encryptedDigestOCTET STRING }

51. PKCS#7 Enveloped data EnvelopedData ::= SEQUENCE { versionINTEGER, recipientInfosRecipientInfos, encryptedContentInfoEncryptedContentInfo } RecipientInfo ::= SEQUENCE { version INTEGER, ISNIssuerAndSerialNumber, keyEncryptionAlgorithmAlgorithmIdentifier, encryptedKeyOCTET STRING } EncryptedContentInfo ::= SEQUENCE { contentTypeContentType, contententEncryptionAlgorithm AlgorithmIdentifier, encryptedContent OCTET STRING OPTIONAL}

52. S/MIME  Secure/Multipurpose Internet Mail Extensions  De facto standard for secure email  Combination of MIME and PKCS #7 –Take a MIME entity –Wrap it in a PKCS #7 structure  Sign or encrypt –Add MIME headers to the result –Repeat if both signature + encryption is to be applied

53. The life cycle of a user certificate Issue Store Use Renew Revoke Register

54. Certificate management  Renew –Like issue, but –You have an old private key –You have a name  Revoke –Sign message  Telephone