Public Key Encryption

a. Public-Key Encryption

b. Building Block: trapdoor permutations

c. Example: RSA

d. Public Key Encryption with a TDF

Cryptography - BBC Archives

Melvyn Bragg and guests discuss the origins and history of codes. In October 1586, in the forbidding hall of Fotheringhay Castle, Mary Queen of Scots was on trial for her life. Accused of treason and denied legal representation, she sat alone in the shadow of a vast and empty throne belonging to her absent cousin and arch rival Elizabeth I of England. Walsingham, Elizabeth’s Principal Secretary, had already arrested and executed Mary’s fellow conspirators, her only hope lay in the code she had used in all her letters concerning the plot. If her cipher remained unbroken she might yet be saved. Not for the first time the life of an individual and the course of history depended on the arcane art of Cryptography.

What are the origins of this secretive science? And what links the ‘Caesar Cipher’ with the complex algorithms which underpin so much of our modern age?

With Simon Singh, science writer and author of The Code Book: The Secret History of Codes and Code-Breaking; Professor Fred Piper, Director of the Information Security Group at Royal Holloway, University of London and co-author of Cryptography: A Very Short Introduction; Lisa Jardine, Professor of Renaissance Studies at Queen Mary, University of London and author of Ingenious Pursuits.

Authenticated Encryption

a. Combining MAC and ENC (CCA)

b. Standards (at a high level)

c. Implementations problems: side channels

d. Generating Randomness (e.g. keys, nonces)

Tracking Cyber Attacks - BBC Archives

Security expert Dave Garfield explains some simple techniques that can be used to track cyber attacks and how attack tasks appear to be split between different groups with different skill sets.

Message Integrity

a. Message Integrity: MACs

b. Secure MACs

c. Construction: ECBC

d. Construction: HMAC (Hash MAC)

e. Construction: PMAC - a parallel MAC

GCHQ Cracking the Code - BBC Archives

The BBC's Security Correspondent Gordon Corera gains unprecedented access to Britain's ultra secret listening station where super computers monitor the world's communications traffic and Britain's global eavesdropping and electronic surveillance operations are conducted.

The layers of secrecy which have surrounded GCHQ's work are peeled away - what exactly does it do and who is it listening to?

The programme explores the wide area covered by signals intelligence - from looking for terrorists planning attacks against the United Kingdom to supporting military operations of the type underway in Afghanistan.

A team from the Counter terrorism section describes what it is like to listen in on terrorists' conversations and the constant battle to predict where the next attack will come from: "I don't think you would be human if you didn't go home at night and couldn't switch off and thought 'Oh my God. What happens if . . .?'" What about the ethics of eavesdropping and how does their work compare to the way it is portrayed on television in series like 'Spooks'?

Code-breakers talk about their work, attempting to find a chink in the armour of a carefully encrypted message sent by a terrorist or a foreign government. "It just feels amazing really," when there is a breakthrough, says one. "I mean you feel like you've won".

The programme looks at the technological challenges posed by the internet and the threat of cyber warfare, which has led to the establishment of a new cyber operations centre at Cheltenham. It also explores the scientific and mathematical breakthroughs which have been achieved at GCHQ, including the discovery of public key encryption, used when we shop on the internet.

There's a tour of the building's four great computer halls, containing racks and racks of IT equipment and covering around ten thousand square metres. "I could actually fit Wembley football pitch into three of the halls quite comfortably,' says the man in charge of making sure that the equipment doesn't crash.

Gordon Corera challenges the director Iain Lobban. There has been considerable speculation about whether the government is planning huge databases at GCHQ to keep track of all communications and internet traffic. Do they really spy on us? And how accountable are they?

Using Block Ciphers

a. Incorrect use of block ciphers

 - In pictures

b. Eavesdropping security: CBC mode

c. Use cases: how to choose an IV
 - Single use key: no IV needed (IV = 0)
 - Multi use key: use a fresh random IV for every message
 - In pictures

d. Eavesdropping security: CTR mode

e. Performance

f. Warning
 - Eavesdropping security is insufficient for most applications
 - Needs also to defend against active attacks
 - CBC and CTR modes are insecure against active attacks