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Cryptology - The practice and study of hiding information

The document presents an overview of cryptography, detailing its objectives of confidentiality, message authentication, integrity, and non-repudiation. It covers key concepts, terminologies, and distinctions between symmetric and asymmetric encryption, alongside specific algorithms like DES, AES, RSA, and elliptic curve cryptography. Additionally, it highlights the real-world applications of cryptography and acknowledges the challenges faced in key distribution and computational efficiency.

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Cryptology The practice and study of hiding information. michael.dance@gmail.com @mikedance
Presentation Goals • Provide a high level overview of cryptography • Clarify the objectives of cryptography • Define the terminology • Explain the basic concepts to build an understanding of how digital security systems, like Bitcoin, are built
Branches • Cryptography • Symmetric Algorithms • Asymmetric (Public Key) Algorithms • Cryptography Protocols • Cryptanalysis
Cryptography Objectives There are four things we are trying to achieve with cryptography.
Confidentiality Information is kept secret from all but the authorised parties.
Message Authentication The sender of a message is authentic.
Message Integrity The message has not been tampered with during transmission.
Non Repudiation The sender of a message cannot deny that they created or sent the message.
Terminology There are around 21 terms you have to know.
Cryptography The science of secret writing with the goal of hiding the meaning of a message.
Cryptanalysis The science and art of breaking crypto systems.
Cipher/Cypher An algorithm for performing encryption and decryption.
Encryption The process of hiding the meaning of a message so only authorised parties can read it.
Decryption The process of restoring a cipher text to the original message.
Channel A communication medium, for example, the internet, mobile/wireless networks, radio waves, etc.
Secure Channel A secure communication medium which can be trusted, used to exchange secret key information, for example, face to face communication.
Insecure Channel An insecure channel is an untrusted communication medium, for example, the internet.
Message The plaintext (readable) message you would like to keep secret.
Cipher Text The encrypted message.
Symmetric Algorithms When encryption and decryption is performed using the same secret key.
Secret Key The data used to encrypt and decrypt in a symmetric algorithm. For example, a password. This must be communicated over a secure channel and kept secret.
Asymmetric/Public Key Algorithms When encryption and decryption is performed using different keys.
Private Key The key used to decrypt a cipher text in a public key algorithm. This must be kept secret.
Public Key The key used to encrypt a message in a public key algorithm. This can be made public.
Key Pair The related public and private keys.
Key Space The set of all possible keys.
Key Size/Length The size measured in bits of the key, this determines the key space required to brute force attack the key.
RNG Random number generator.
PRNG Pseudo Random Number Generator is a RNG that is not truly random, used when security is not a concern, for example with video games.
CSPRNG A cryptographically secure pseudo-random number generator. Used for cryptography applications, for example generating a bitcoin private key.
THE END. Of the terminology.
Real World Crypto Systems
Kerckhoffs’ Principle A crypto system should be secure even if the attacker knows all the details about the system, with the exception of the secret key.
Symmetric Crypto Systems Uses one secret key for encryption and decryption
Analogy A safe with one lock where each person with access has a copy of the same key
DES • Data Encryption Standard • The most popular and best studied block cipher of the last 30 years • Proposed in 1974 in response to a NIST (National Institute of Standards and Technology) request for a standardised cipher to secure government and national security communications • Proposed by IBM cryptographers, with input from the NSA with no public discourse • Insecure due to small key space
3DES • Triple DES • Performs DES encryption 3 times, which yields a more secure cipher • Still widely used primarily due to legacy implementations and hardware • Software implementations are not very efficient
AES • Advanced Encryption Standard • The most widely used symmetric cipher today • In 1997, an open worldwide competition was held where cryptography algorithms were submitted and reviewed by the international scientific community • In 2001, the Rinjdael cipher, created by two young Belgian cryptographers was selected for AES over submissions from IBM, RSA, and several famous cryptographers • In 2003, the NSA announced it will allow AES encryption to be used for classified top secret documents • Used in Blockchain.info wallets, Mac FileVault, Skype, WIFI encryption, IPSec, TLS, SSH, etc. • No known attacks have been found
Symmetric Pitfalls • Key Distribution Problem • A copy of the key must be exchanged over a secure channel, problematic to do over the internet! • The number of keys required can get very large • Non repudiation is not possible because several people may use the same key
Asymmetric/Public Key Crypto Systems Uses a public key for encryption and a private key for decryption.
Analogy A mailbox on the street, everyone can put a letter in (encrypt), but only a person with a private (secret) key can retrieve the letters (decrypt).
Background • Symmetric cryptography has been around for as long as written language, public key cryptography is very new • Public key cryptography was publicly introduced in 1976 by Whitfield Diffie, Martin Hellman, and Ralph Merkle
Overview • Solves the key exchange problem because the encryption key can be public (hence the name, public key) • Can be used to prove the authenticity and integrity of a message using digital signatures, and a digital signature algorithm (non repudiation) • Can be used to identify entities using challenge and response protocols together with digital signatures, for example, electronic car keys, passports, or bank cards • Relies on one way functions, which is easy to compute in one direction, but the inverse computation is computationally infeasible
RSA • Published in 1977 by Ron Rivest, Adi Shamir and Leonard Adleman • Security is provided by the integer factorisation problem • Given two large primes, it is easy to compute the product, but difficult to factor the resulting product • Requires large key sizes to be secure with modern day computers, which is problematic for smaller devices like mobile phones, smart cards, etc.
Elliptic Curve Cryptography • Introduced in 1985 by Neal Koblitz and Victor S. Miller, algorithms entered wide use in 2004, and 2005 • Uses elliptic curve over finite field mathematics to generate public and private keys • Security is provided by the elliptic curve discrete logarithm problem • Provides roughly the same security of RSA with large key sizes, with much smaller key sizes, which is leading to adoption in mobile phones, and smart cards • Bitcoin uses private and public key pairs based on ECC
Asymmetric Pitfalls • Encryption is significantly more computationally expensive than symmetric algorithms
In reality A hybrid approach is used by using a public key algorithm (which is slower) to encrypt and exchange a symmetric key (which is small), a symmetric algorithm (which is fast) can then be used to encrypt the message (which is big).
The End Of part 1
What’s Next? • Digital Signatures and Hash Functions • Elliptic Curve Cryptography • Bitcoin Cryptography
Questions? michael.dance@gmail.com @mikedance
Further Reading • Understanding Cryptography by Christof Paar and Jan Pelzl (http://www.crypto-textbook.com/) • Cryptography Lectures • https://www.youtube.com/playlist? list=PLoJC20gNfC2gAB-eg7oaUTheB_JgQY4-q • Public Key Cryptography: Diffie-Hellman Key Exchange • https://www.youtube.com/watch?v=3QnD2c4Xovk
Cryptology - The practice and study of hiding information