The subject of e-security is now so far removed from the relatively simple fields of household and personal security that it can prove to be an intimidating minefield for those who are unaware of the tools of the trade – and ways of counteracting them.
Such methods as data encryption and sender authenticity are used to combat cyber hackers, of course, but what do these terms mean? Security staff need to know if they’re to combat threats to a company’s business in today’s Web-enabled Brave New World.
Essentially, there are two main types to consider when tackling the subject of encryption: symmetric and asymmetric (or public and private) key crypto-systems. These systems are instrumental in building e-commerce security solutions, and can be used to achieve confidentiality, integrity, authenticity and – most importantly – irrefutable proof of electronic data transfer.
Symmetric key encryption is the oldest and most widely known method. With this particular type of encryption, plain text is transformed using a secret key (encrypting/decrypting tool) into random-looking encrypted data from which no information can be retrieved without that same key. Only with this ‘secret’ key can one decrypt the coded data into its original plain text format.
As a result, e-mails encrypted in this way can be stored at – or transmitted through – places to which others might have access. Since the secret key used for encryption and that used for the decryption process coincide, this type of encryption is aptly-named ‘symmetric key encryption’. Metaphorically speaking, it can be likened to a combination safe.
The fact that an encrypted document is only decipherable by the fellow key holder provides absolute assurance as to the authenticity of the sender and the integrity of the document (provided, of course, that the sender is certain he/she and the receiver are the only two parties with access to the common secret key).
Irrefutable proof of authenticity cannot be provided by using symmetric key systems alone, as a receiver who alleges that a person sent him/her a document could well have lied and sent it to themselves. To achieve complete authenticity, security staff must look towards using asymmetric key systems.
Asymmetric key systems explained
Again speaking metaphorically, asymmetric (or ‘public’) key encryption might be viewed as a combination ‘safe’ having two combination locks: one to close the safe, the other to open it. In truth, these combinations are different – the locking key combination cannot open the safe on its own, while that for the opening key cannot close it on its own.
Let’s look at a simple example by way of explanation. If person A (Alice) wants to send a confidential document to person B (Bob), then Alice needs to ask Bob for his ‘close’ key. Alice will then put the document in the safe, and close it using Bob’s close key. Subsequently, only with the ‘open’ key (in Bob’s possession) can the closed safe be reopened. Even Alice cannot open the safe again. In practice, Bob will publish his close key in a directory, such that the close key is also called the ‘public key’, as opposed to the ‘private key’ (which is able to open all safes closed with Bob’s public key).
The authenticity of public keys: PKIs
In applications of asymmetric encryption (ie confidentiality and digital signatures), authenticity of the public key is crucial.
For instance, if person C (Emma) is able to replace Bob’s public key (eg in transit, or in a directory) with a private key about which Emma has no knowledge, then documents encrypted by Alice using Bob’s alleged public key will actually be readable by Emma.
Subsequently, Emma could intercept and stop the encrypted document, retrieve it by using a corresponding private key, encrypt the document again with Bob’s valid public key and send this newly-encrypted document through to him.
Perhaps neither Alice nor Bob might notice that Emma is reading the documents. A similar problem arises with the use of asymmetric encryption for digital signatures.
The point is that, before relying on someone else’s public key, one should be confident about the ‘binding’ of the key – not to mention the identity of the private key’s owner.
Using hybrid encryption
Asymmetric encryption is far more computationally difficult than its symmetric counterpart, such that security/IT managers should perform as few asymmetric encryptions/decryptions as possible. To help them in their endeavours, they could use the hybrid encryption technique: a combination of asymmetric and conventional encryption.
Referring once again to our hypothetical scenario, instead of asymmetrically encrypting the whole document with Bob’s public key, Alice would generate a random secret (or ‘session’) key, encrypting the entire document by using a symmetric key system and then asymmetrically encrypt the secret key with Bob’s public key.
Decryption would be carried out in a similar fashion. Using his private key, Bob would asymmetrically decrypt the secret key, and then decrypt the whole document using both the secret key and the symmetric key system. In simple terms, hybrid encryption uses two ‘safes’ instead of one: one is symmetric, the other asymmetric.
Companies including PrivateExpress and ZixMail offer this service to security managers, so too Wellance with its Regedoc service.
Security is a subject that affects us all in different ways, according to the nature of the business we’re protecting and the basic model that lies behind it. Admittedly, the necessary funding required to ensure an absolutely ‘hack-free’ network can be costly for the end user, but surely the risk of not investing in one is potentially far more dangerous…isn’t it?
Steve Rawsthorn is chief marketing officer at Wellance.
