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Choosing Encryption Algorithms

Updated Jan 30, 2024 ·

Overview​

There are many encryption algorithms, each with its own strengths and weaknesses. Choosing the right one requires understanding how it aligns with the four primary goals of cryptography (Confidentiality, Integrity, Authentication, and Non-repudiation) and the potential flaws that could affect security.

Encryption uses complex mathematical techniques, and even minor flaws can create vulnerabilities. It is generally unwise to create your own encryption unless you have deep expertise. Be wary of vendors claiming proprietary algorithms without sharing details, as this can be a security risk.

For robust security, select algorithms that have been thoroughly tested and vetted by the security community. This scrutiny ensures they are well-designed and free of vulnerabilities or hidden backdoors.

Key Considerations​

  • Proven Algorithms

    • Choose algorithms with extensive public evaluation.
    • Ensure acceptance in the security community.

  • Key Length

    • Longer keys are more secure by making them harder to guess.
    • Longer keys can reduce performance.
    • Balance security with system speed.

  • Vulnerability to Brute Force

    • Longer keys increase possible combinations.
    • Makes them more resistant to brute-force attacks.

Key Length​

Consider if the algorithm allows for adjustable key lengths. While longer keys are more secure, they can affect performance, requiring a trade-off between security and speed. A 40-bit key might seem complex with over a trillion combinations, but modern computers can break it. A 128-bit key offers more security, and a 1024-bit key provides even stronger protection.

Ultimately, selecting an encryption method involves balancing security needs with performance requirements through careful analysis of key length and algorithm choice.

A Perfect Cipher​

Imagine having an encryption method that no one could ever break. Over a century ago, a telegraph expert developed such a method: the one-time pad. This cipher is truly unbreakable and has stood the test of time.

Encrypting the Message​

The one-time pad relies on simplicity and randomness. Both the sender and the receiver use pads filled with random letters that are identical.

  • The pad must be as long as all the messages exchanged.
  • A page from the one-time pad might look like a series of random letters.

To encrypt a message, you write it in plaintext on the pad. For example, the word "secret" would be written across the top of the pad. The process involves combining the letters of the message with the key, treating them as numbers: A is 1, B is 2, etc.

  • Encrypt the first letter, S, by adding A (1) to get T.
  • Next, add E and C (3), moving E to F, G, H.
  • Combine C and G to get J.

Sometimes, you need to wrap around the alphabet. For example, adding L (12) to R involves looping around to get D.

Decrypting the Message​

To decrypt, the receiver subtracts the key from the message:

  • Begin by writing the encrypted message: T, H, J, D, P, V.
  • Subtract the key to reveal the original message:
    • T minus A becomes S.
    • H minus C becomes E.
    • J minus G becomes C.

For tricky cases like D minus L, wrap backward around the alphabet to get R. Continue until you uncover the full message: "Secret."

Challenges​

Despite its perfect security, the one-time pad isn't commonly used due to practical issues:

  • Both parties need to exchange pads in person to maintain security.
  • They must meet again when the pad pages are used up, making it inconvenient for frequent exchanges.

While the one-time pad offers perfect encryption, these challenges make it less practical for widespread use today.

Cryptographic Lifecycles​

Cryptographic algorithms and keys are essential for securing information. Understanding how to manage these systems throughout their lifecycle is key for adapting to changing security needs and threats.

Over time, algorithms can become less secure due to flaws or vulnerable key lengths. Managing them through a lifecycle approach helps phase out outdated systems and maintain security.

NIST’s Five-Stage Lifecycle​

  1. Initiation

    • Recognize the need for a new cryptographic system and gather requirements.
    • Focus on confidentiality, integrity, and availability based on information sensitivity.

  2. Development/Acquisition

    • Acquire or develop a system with suitable software, hardware, algorithms, and keys.

  3. Implementation and Assessment

    • Configure the system and assess if it meets security objectives.

  4. Operations and Maintenance

    • Ensure the system operates securely throughout its use.

  5. Sunset

    • Decommission the system and handle sensitive materials, such as keys, appropriately.

Digital Rights Management (DRM)​

DRM technologies are designed to prevent unauthorized use of digital content, protecting intellectual property from theft and piracy.

  • Purpose

    • Protect content through encryption to prevent unauthorized access.
    • Used in music, movies, books, video games, and other digital media.

  • Example

    • Apple initially used FairPlay DRM for music on iTunes but later switched to DRM-free music. Now, DRM is used to control access in subscription-based services, allowing revocation if the subscription is canceled.

  • Application

    • DRM technologies are also applied to other media like e-books and video games.
    • Businesses use DRM to safeguard trade secrets, control access, and limit redistribution of sensitive information.