10 – 12 APRIL 2005 Riyadh, Saudi Arabia

Encryption in Detail: The Inner Workings Murat Lostar NOSPAM com) Information Security Consultant

Cryptography The art of secret message writing. Creating texts that can only be read by authorized individuals only.

Simple Cryptography   Plaintext Key Ciphertext

Caesar Cipher ABCDEFGHIJKLMNOPQRSTUVWXYZ NOPQRSTUVWXYZABCDEFGHIJKLM THE GOTHS COMETH rotate 13 positions FUR TAFUE PAYRFU Plaintext Key Ciphertext 13

ABCDEFGHIJKLMNOPQRSTUVWXYZ BCDEFGHIJKLMNOPQRSTUVWXYZA CDEFGHIJKLMNOPQRSTUVWXYZAB DEFGHIJKLMNOPQRSTUVWXYZABC EFGHIJKLMNOPQRSTUVWXYZABCD FGHIJKLMNOPQRSTUVWXYZABCDE GHIJKLMNOPQRSTUVWXYZABCDEF HIJKLMNOPQRSTUVWXYZABCD... Rotating Key Cipher SOUND THE RETREAT DEADFED VSUPC XKG UEWWEX plaintext key ciphertext

General Principles Longer keys make better ciphers Random keys make better ciphers Good ciphers produce “random” ciphertext Best keys are used once and thrown away

Symmetric (Private Key) Cryptography 8 Examples: AES, DES, RC5, IDEA, Skipjack Advantages: fast, ciphertext secure Disadvantages: must distribute key in advance, key must not be disclosed

DES: Data Encryption Standard Widely published & used - federal standard Complex series of bit substitutions, permutations and recombinations Basic DES: 56-bit keys Crackable in about a day using specialized hardware Triple DES: effective 112-bit key Stronger

AES (Rijndael) Standard replacement for DES for US government, and, probably for all of us as a result… Winner of the AES (Advanced Encryption Standard) competition run by NIST (National Institute of Standards and Technology in US) in Comes from Europe (Belgium) by Joan Daemen and Vincent Rijmen. “X-files” stories less likely (unlike DES). Symmetric block-cipher (128, 192 or 256 bits) with variable keys (128, 192 or 256 bits, too) Fast and a lot of good properties, such as good immunity from timing and power (electric) analysis Construction deceptively similar to DES (XORs etc.) but really different

Asymmetric (Public Key) Cryptography 8 8 u Examples: RSA, Diffie-Hellman, ElGamal u Advantages: public key widely distributable, does digital signatures u Disadvantages: slow, key distribution

RSA Algorithm patented by RSA Data Security Uses special properties of modular arithmetic C = P e (mod n) P = C d (mod n) e, d, and n all hundreds of digits long and derived from a pair of large prime numbers Keys lengths from 512 to 4096 bits

Symmetric vs. Asymmetric Encryption Algorithm TypeDescription Symmetric (DES, TripleDES, AES, IDEA, RC2…) Uses one key to: Encrypt the data Decrypt the data Is fast and efficient Requires secure transfer of key Asymmetric (RSA, DH, DSA, ElGammal) Uses two mathematically related keys: Public key to encrypt the data Private key to decrypt the data Is slower than symmetric encryption Solves key distribution problem Hybrid (RSA/AES etc.) Symmetric encryption of data Asymmetric encryption of the symmetric key

Hybrid Encryption (Real World) As above, repeated for other recipients or recovery agents Digital Envelope Other recipient’s or agent’s public key (in certificate) in recovery policy Launch key for nuclear missile“RedHeat”is... Symmetric key encrypted asymmetrically (e.g., RSA) Digital Envelope User’s public key (in certificate) RNG Randomly- Generated symmetric “session” key Symmetric encryption (e.g. DES) *#$fjda^ju539!3t t389E 5e%32\^kd

*#$fjda^ju539!3t 5e%32\^kd Launch key for nuclear missile“RedHeat”is... Launch key for nuclear missile“RedHeat”is... Symmetric decryption (e.g. DES) Digital Envelope Asymmetric decryption of “session” key (e.g. RSA) Symmetric “session” key Session key must be decrypted using the recipient’s private key Digital envelope contains “session” key encrypted using recipient’s public key Recipient’s private key Hybrid Decryption

Public Key Encryption: The Frills Frill (add-on)Technique Fast encryption/decryptionDigital envelopes Authentication of senderDigital signature Verification of message integrityMessage digests Safe distribution of public keysCertifying authorities

Digital Envelopes 88 session key public key private key

Digital Signatures 88 public key private key

Message Digests sender’s public key sender’s private key hash

Verifying Simple Data Integrity with Hashes (Message Digests) User A User B Data Hash Value Hash Algorithm Data Hash Value Hash Algorithm If hash values match, data is valid User A sends data and hash value to User B

Creating a Digital Signature Hash Function (SHA, MD5) Jrf843kjfgf* £$&Hdif*7o HDFHSD(** Py75c%bn&*)9|fDe^b mdFg$5knvMd’rkveg Ms” This is a really long message about Bill’s… Asymmetric Encryption Message or File Digital Signature 128 bits Message Digest Calculate a short message digest from even a long input using a one-way message digest function (hash) Signatory’s private key private

Verifying a Digital Signature Jrf843kjf gf*£$&Hd if*7oUsd FHSD(** Py75c%bn&*) 9|fDe^bDFaq &nmdFg$5kn vMd’rkvegMs” Asymmetric decryption (e.g. RSA) Everyone has access to trusted public key of the signatory Signatory’s public key Digital Signature This is a really long message about Bill’s… Same hash function (e.g. MD5, SHA…) Original Message Py75c%bn&*) 9|fDe^bDFaq &nmdFg$5kn vMd’rkvegMs” ? == ? Are They Same?

Certifying Authorities

X.509 Certificate Certificate Authority Digital Signature of All Components Together: Serial Number Issuer X.500 Distinguished Name Validity Period Subject X.500 Distinguished Name Subject Public Key Information Key/Certificate Usage Extensions OU=Project Botticelli… The Key or Info About It

Hierarchy of Trust

Transmitting Public Keys 8 8

Future is Here: Quantum Cryptography Method for generating and passing a secret key or a random stream Not for passing the actual data, but that’s irrelevant Polarisation of light (photons) can be detected only in a way that destroys the “direction” (basis) So if someone other than you observes it, you receive nothing useful and you know you were bugged Perfectly doable up to 120km long fibre-optic link Commercial applications available as of Nov 2003 (BB84) Don’t confuse it with quantum computing, which won’t be with us for at least another 50 years or so, or maybe longer…

For more information The Code Book (Simon Singh) ISBN: RSA ( Applied Cryptography, B. Schneier, John Wiley & Sons, ISBN Foundations of Cryptography, O. Goldereich, Books/oded_book_readme.html Books/oded_book_readme.html

© 2005 Microsoft Corporation. All rights reserved. This presentation is for informational purposes only. MICROSOFT MAKES NO WARRANTIES, EXPRESS OR IMPLIED, IN THIS SUMMARY.