Enhancing Email Security with S/MIME

1. Enhancing Email Security with S/MIME Chuck Connell, www.chc-3.com www.DominoAdministration.com, www.DominoSecurity.org

2. Introduction • Worked at Lotus from 90 to 95 • Managed Notes C API team, architect in (short-lived) “enterprise applications” group, business partner technical liaison • Began my own business in 1995 • Notes/Domino consulting, writing, teaching CS at Boston University • Security expert at www.SearchDomino.com

3. Outline • What is S/MIME? • Why do we care about it? • Secrecy, authentication, and integrity • Cryptography primer, including public key techniques and certificates • How S/MIME works • Where S/MIME is used in Notes/Domino • How to use S/MIME

4. Audience • Experienced with Notes, Domino, general email topics • Used some encryption/privacy tools • Not a security expert or mathematician (will skip gory details) • My goal is to explain a fairly complex topic to a generally knowledgeable computer audience

5. What is S/MIME? • When email was first developed, people could only send plain text messages • MIME was developed in early 90s to allow people to send pictures, sound, programs and general attachments -- “Multipurpose Internet Mail Extension” • MIME has no security features, can be read along its route or forged (easily) • S/MIME is a secure version of MIME

6. What does S/MIME give us? • Secrecy – Only intended recipient can read the message. (A thick envelope and trustworthy couriers.) • Authentication – Recipient knows the message came from the apparent sender. (An ink signature that you recognize.) • Integrity – Recipient knows the message was not changed en route. (Un-erasable ink in a letter.)

7. Cryptography primer • Secret key (a.k.a symmetric cipher) • Public key (a.k.a. asymmetric cipher) • Secrecy • Authentication • Secrecy and authentication • Hashing (a.k.a. message digest) • Public key certificate (X.509)

8. Symmetric cipher • Dates back thousands of years • A “key” is scrambled into the message in a way that makes the message unreadable • Scrambling method can be pencil and paper, mechanical, or mathematical • Key can be numbers, letters, text from a book • Only way to read the message (easily) is to unscramble it with the same key • Sender and receiver must exchange key somehow

9. Symmetric cipher

10. Public key cryptography (PKC) • Invented in 1970s • There are two keys; one public for all to see, the other kept secret to one person • Keys are pairs of large numbers, related to prime number theory • Message is scrambled with one key; only unscrambled easily with the other key • Can be used for secrecy, authentication, or both

11. Public key cryptography

12. PKC for secrecy only • Chuck wants to send message that only Katie can read • Ciphertext = PKC(plaintext, katie’s public key) • Plaintext = PKC(ciphertext, katie’s private key) • Only Katie can decrypt the message, and Chuck does not have to send her a key

13. PKC for authentication only • Chuck wants to send message to Katie and prove it is from him • Ciphertext = PKC(plaintext1, chuck’s private key) • Chuck sends ciphertext and plaintext1 • Plaintext2 = PKC(ciphertext, chuck’s public key) • Katie compares plaintext1 (sent) with plaintext2 (decrypted) • If they match, only Chuck could have sent the message.

14. PKC for secrecy and authentication • Chuck wants to send secret message to Katie and prove it is from him • Cipher1 = PKC(plaintext1, chuck’s private key) • Cipher2 = PKC(Cipher1 and plaintext1, katie’s public key) • Chuck sends Cipher2 • Cipher1 and Plaintext1 = PKC(Cipher2, katie’s private key) • Plaintext2 = PKC(Cipher1, chuck’s public key) • Katie compares plaintext1 (sent) with plaintext2 (decrypted)

15. Hashing • A one-way operation that is hard to undo • Often results in a shorter message, which is called a message digest • Example: “Let’s have breakfast at Dunkin Donuts”  “h7tfd8Fr”

16. Public key certificate • But, there is a problem with PKC… How does Katie know it is really Chuck sending her the message. Someone could pretend to be Chuck. • Public key certificates solve this problem (mostly) • A public key certificate contains • A person’s name • That person’s public key • Name of a trusted certifying authority (CA) • Digital signature of the CA, using their private key • Certificate can be verified with CA’s public key • X.509 is most common format

17. Questions ?

18. So what is S/MIME? • S/MIME puts all these techniques together to create a practical, efficient, reasonably secure email protocol • Standard (symmetric) cipher – RC2 or TripleDES • Public key (asymmetric) cipher – RSA • Hashing – SHA-1 or MD5 • (Mathematical details found in references)

19. S/MIME for secrecy only • Chuck’s email program creates a random key (session key) to be used in a symmetric cipher. • Chuck’s email program encrypts the message with the symmetric cipher and session key. • Chuck’s email program encrypts the session key with PKC and Katie's public key. • Chuck’s email program creates a package of: encrypted message, encrypted session key, his X.509 certificate, names of encryption algorithms.

20. S/MIME for secrecy, continued • Chuck’s email program sends package to Katie. This is an S/MIME email message. • Katie’s email program receives package. • Katie's email program uses her private key (and named PKC method) to decrypt the session key. • Katie’s email program uses session key (and named symmetric cipher) to decrypt the message.

21. S/MIME for authentication only • Chuck’s email program uses hash function to create message digest • Chuck’s email program encrypts message digest with PKC and his private key • Chuck’s email program creates a package of: original message, encrypted message digest, his X.509 certificate, names of encryption algorithms • Chuck’s email program sends package to Katie. • Katie's email program receives package

22. S/MIME for authentication, continued • Katie’s email program verifies Chuck’s X.509 certificate by testing signature of CA • Katie’s email program gets Chuck’s public key from his certificate • Katie's email program uses Chuck’s public key to decrypt the message digest • Katie's email program independently computes the message digest, using the same hash function • Katie's email program compares the two message digests to verify sender and message integrity

23. S/MIME for secrecy and authentication • Message is authenticated just as shown above • Authenticated package is made secret, just as shown above • Secret package is sent to recipient • Receiver uses his/her private key to decrypt session key • Receiver uses session key to decrypt rest of secret package, yielding authenticated message • Receiver authenticates message, just as shown above

24. Questions ?

25. So S/MIME is used for Notes mail? • No! For pure Notes email (Notes and Domino) S/MIME is not needed. Notes has its own, similar, methods. • S/MIME is used whenever pure Notes email is not available • From Notes, through Domino, to other email • From Notes, through standard server, to any email • From other email, through Domino, to any email

26. Using S/MIME • Get a digital identification • Set up Domino server for S/MIME • Use S/MIME with general email clients • Use S/MIME with Notes

27. Getting a digital identification • A digital ID is • Your name • Public/private key pair • Public key certificate for this ID • Most popular vendors are www.Thawte.com and www.VeriSign.com • Thawte is free, but VeriSign is only $15/year and simpler to use

28. Setting up Domino for S/MIME • Do nothing! (other than standard Internet mail set up) • (If anyone is aware of special settings that are required, please let me know.)

29. S/MIME with standard email clients (e.g. Outlook Express) • If you got your digital ID on this computer, it is already installed (Can see the ID with Start / Settings / Control Panel / Internet Options / Content / Certificates) • For secrecy, just press Encrypt • For authentication, just press Sign • When receiving a message, you will see security symbols near the attachment paperclip

30. Using S/MIME with Notes (Assuming digital ID already on Windows computer) • Export digital ID from Windows • Import digital ID to Notes ID file • Make sure this certificate will be used for Internet mail from Notes • Use digital ID as you send and receive email Demonstration…

31. For further reading • Excellent online overview of cryptography: www.rsalabs.com/faq/ • Cryptography and Network Security by William Stallings – Good general security textbook. www.amazon.com/exec/obidos/ASIN/0138690170 • S/MIME Internet task force: www.imc.org/ietf-smime/index.html • Relationship between S/MIME and PGP/MIME: www.imc.org/smime-pgpmime.html