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#MoreCrypto : Introduction to TLS


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A very brief introduction to TLS, delivered at the #MeraKrypto event in Stockholm April 29th, 2014.

Published in: Technology, Education

#MoreCrypto : Introduction to TLS

  1. 1. TLS in five minutes #MeraKrypto @oej *
 v 1.1 2014-05-06
  2. 2. #MoreCrypto Identity Security basics. Confidentiality Authorization Integrity Non-repudiation
  3. 3. #MoreCrypto TLS is an important tool TLS Transport
 Security TLS provides confidentiality, identity
 and integrity to Internet communication. TLS is used in HTTPS:// web pages, but can also be used from applications on a computer as well as a cell phone. TLS is based on SSL, that was a provider-specific technology. TLS is maintained by the IETF and is still being improved.
  4. 4. TLS basics in a minute • TLS use a keypair to set up a secure connection • Assymetric encryption • The server sends the public key at connection • The client challenges the server • The server responds to the challenge using the server private key • Now the client knows that the server has the private key that matches the public key private
  5. 5. TLS Usage • TLS is used for • authentication of servers and clients • initiating encryption of a session • digital signatures on messages to ensure integrity and provide authentication Authentication Who are you? Prove it! Encryption Providing confidentiality Integrity Making sure that the receiver get what the sender sent
  6. 6. Adding a certificate to the mix • A certificate is nothing more complicated than a passport or an ID card • It contains the public key and some administrative data • And is signed (electronically) by someone you might trust ... or not. • This is part of the complex structure called PKI, which you might want or just disregard • A PKI is not needed to get encryption for the signalling path! • You can however use a PKI to only set up connections that you trust
  7. 7. The X.509v3 certificate • An X.509 certificate is the standardised way to
 bind a public key to an identity • The certificate is issued by a 
 Certification Authority (CA) • The most important component of the PKI? • An X.509 certificate is an 
 electronic document with a specific layout ! • Standard: documented in IETF PKIX RFC:s Version Serial number Issuer identity Validity period User identity Public key Extension fields
  8. 8. X509.v3
 contents • Version number • Certificate serial number
 Used for validation • Identity of the issuer • Validity period • Identity of the public key owner • Public key • Extension fields • A digital signature, created by the issuer Internet
  9. 9. SIP certificates • SubjectAltName contains a list of identities that are valid for this certificate • draft-ietf-certs outlines a SIP event package to distribute and manage certificates • This is based on the Authentication Service in SIP identity (RFC 4474) • The domain cert is used to sign the NOTIFY payload
  10. 10. x.509 cert for SIP Certificate: Data: Version: 3 (0x2) Serial Number: 01:08:00:79:00:15:00:43 Signature Algorithm: sha1WithRSAEncryption Issuer: C=US, ST=California, L=San Jose, O=sipit, OU=SipitTest Certificate Authority Validity Not Before: Sep 16 17:17:00 2009 GMT Not After : Sep 15 17:17:00 2012 GMT Subject: C=US, ST=California, L=San Jose, O=sipit, Subject Public Key Info: Public Key Algorithm: rsaEncryption RSA Public Key: (2048 bit) Modulus (2048 bit): 00:a7:96:65:6e:b6:ba:3a:48:a1:bd:a3:ae:21:dc: a8:92:97:3c:43:ea:24:e6:9f:93:2f:61:7e:d3:2d: 30:1e:21:42:b9:d6:59:87:f1:b1:f8:c8:39:8e:43: 64:9a:31:2c:18:3d:cd:d8:03:64:bb:14:38:44:05: 20:30:d8:e1:db:a7:4d:c3:47:a2:49:73:d1:10:ed: 2f:cf:74:26:57:91:64:af:b0:f2:5d:3f:88:9f:df: 65:6c:ba:65:3f:66:99:52:6b:20:d2:0e:e3:65:18: b1:8e:3d:ca:f2:4a:45:c5:4d:85:ef:82:54:f8:54: 54:db:96:90:9b:c5:1b:2a:1e:60:3c:43:71:55:60: 30:93:8f:fd:d8:d9:3d:a1:32:e3:56:4b:e2:73:b6: cc:18:93:8a:d8:8b:68:81:c7:fd:cd:d5:dc:4c:a2: 86:61:9f:ad:d0:b1:d3:3c:4c:6c:07:54:b2:43:b4: a7:0a:0a:f2:e3:6d:12:43:16:70:63:c9:e9:1a:78: 66:9d:ee:30:94:7b:ab:f2:e9:67:4a:66:6d:8c:ed: a8:a4:98:51:77:0b:a7:60:55:73:85:87:4a:57:6b: 24:fe:27:00:02:79:70:da:5a:45:ad:aa:3d:d5:40: 5b:5c:85:63:93:56:af:c7:e8:e3:b6:1a:25:b6:a2: 2d:37 Exponent: 65537 (0x10001) X509v3 extensions: X509v3 Subject Alternative Name:,, X509v3 Basic Constraints: CA:FALSE X509v3 Subject Key Identifier: 27:F7:A9:96:F5:B2:8F:0B:5E:A9:C7:F5:0F:AC:3D:AB:3D:8D:F0:30 Signature Algorithm: sha1WithRSAEncryption 1a:fe:1f:af:86:99:82:e5:14:97:8d:64:9a:d1:5c:ea:6c:96: f5:c6:0c:7d:20:5f:4e:70:05:24:3a:de:b5:b9:cf:66:8d:4c: 74:d5:6a:a9:52:74:17:bc:b4:79:a0:58:32:78:a9:70:7c:6a: 15:ac:07:29:77:13:06:55:53:3f:0b:4c:3d:da:55:6e:ad:74: 56:01:55:c8:4c:19:8d:06:0b:f3:4c:04:d5:9a:6f:44:ad:7a: fd:3b:aa:e8:4b:84:6e:f1:c4:34:f4:a0:6a:f6:81:ae:74:b4: 46:6e:b9:2f:a6:59:f1:02:e9:58:7c:a1:8d:08:31:2b:39:ee: eb:7e Subject: C=US, ST=California, L=San Jose, O=sipit, X509v3 Subject Alternative Name:,,
  11. 11. Process for a server Generate
 Keys Pack public key
 in CSR Send CSR
 to CA CA validate
 process CA issues 
 Certificate Install cert
 in server with
 private key
  12. 12. Client connection Open TCP
 connection Server sends
 certificate Client
 challenge server Server answers
 challenge Client validates
 certificate Server can issue
 cert request Client and server produce session key Symmetric encryption starts
  13. 13. Protocol specifics • Given a protocol request - how do we match the request address to a certificate • SIP Uri, E-mail address, HTTPS uri
  14. 14. User specifics • Which CAs do we trust? • How do we check validity of certificate, even if we trust the CA? • Do we have time for validation?
  15. 15. New solutions • Anchoring the certificate in DNS • Validating the certificate in DNS • No certificate - bare keys • Oppurtunistic Security with TLS