Define cryptography. How can cryptography works as security tool?

Subject Computer and Network Security
NU Year Set: 1.(a) Marks: 1+2=3 Year: 2017

Cryptography is associated with the process of converting ordinary plain text into unintelligible text and vice-versa. It is a method of storing and transmitting data in a particular form so that only those for whom it is intended can read and process it. Cryptography not only protects data from theft or alteration, but can also be used for user authentication.

Managing keys requires three considerations:
  1. Where will you store them?
  1. How will you ensure they are protected but available when needed?
  1. What key strength is adequate for the data protected?
Key Storage
Many organizations store key files on the same system, and often the same drive, as the encrypted database or files. While this might seem like a good idea if your key is encrypted, it is bad security. What happens if the system fails and the key is not recoverable? Having usable backups helps, but backup restores do not always work as planned…
Regardless of where you keep your key, encrypt it. Of course, now you have to decide where to store the encryption key for the encrypted encryption key. None of this confusion is necessary if you store all keys in a secure, central location. Further, do not rely solely on backups. Consider storing keys in escrow, allowing access by a limited number of employees (“key escrow,” n.d.). Escrow storage can be a safe deposit box, a trusted third party, etc. Under no circumstances allow any one employee to privately encrypt your keys.
Key Protection
Encrypted keys protecting encrypted production data cannot be locked away and only brought out by trusted employees as needed. Rather, keep the keys available but safe. Key access security is, at its most basic level, a function of the strength of your authentication methods. Regardless of how well protected your keys are when not used, authenticated users (including applications) must gain access. Ensure identity verification is strong and aggressively enforce separation of duties, least privilege, and need-to-know.
Key Strength
Most, if not all, attacks against your encryption will try to acquire one or more of your keys. Use of weak keys or untested/questionable ciphers might achieve compliance, but it provides your organization, its customers, and its investors with a false sense of security. As Ferguson, Schneier, and Kohno (2010) wrote,
In situations like this (which are all too common) any voodoo that the customer [or management] believes in would provide the same feeling of security and work just as well (p. 12).
So what is considered a strong key for a cipher like AES? AES can use 128-, 192-, or 256-bit keys. 128-bit keys are strong enough for most business data, if you make them as random as possible. Key strength is measured by key size and an attacker’s ability to step through possible combinations until the right key is found. However you choose your keys, ensure you get as close as possible to a key selection process in which all bit combinations are equally likely to appear in the key space (all possible keys).

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