Objective 1.4High Priority10 min read

Encryption Algorithms and Key Length

Common encryption algorithms (AES, RSA, 3DES, etc.) and understanding how key length affects security strength. Longer keys generally provide stronger encryption, but different algorithm types require different key lengths for equivalent security.

Understanding Encryption Algorithms and Key Length

Encryption algorithms are the mathematical procedures that transform plaintext into ciphertext. Key length (measured in bits) determines how many possible keys exist—longer keys mean more possibilities to try, making brute-force attacks impractical.

Key principle: Longer keys = more security, but different algorithm types need different key lengths for equivalent security. AES-128 is roughly equivalent to RSA-3072 in security strength.

Choosing the right algorithm and key length depends on the use case, performance requirements, and how long the data needs protection. Algorithms considered secure today may be broken in the future, especially with quantum computing advances.

Why This Matters for the Exam

SY0-701 tests your knowledge of common algorithms and appropriate key lengths. Questions may ask which algorithm is appropriate for a scenario, what key length provides adequate security, or which algorithms are deprecated.

Understanding algorithms helps with compliance questions—regulations often specify minimum key lengths. PCI DSS, HIPAA, and government standards all have cryptographic requirements.

This knowledge is also practical: choosing weak algorithms or short keys is a common security mistake in real implementations.

Deep Dive

Symmetric Algorithms

AES (Advanced Encryption Standard)

  • •Current standard symmetric algorithm
  • •Key sizes: 128, 192, or 256 bits
  • •Block cipher (128-bit blocks)
  • •Very fast and secure
  • •Used almost everywhere

3DES (Triple DES)

  • •Applies DES three times
  • •Effective key length: 112 or 168 bits
  • •Deprecated — slow and has vulnerabilities
  • •Being phased out

Blowfish/Twofish

  • •Alternative to AES
  • •Variable key length up to 448 bits (Blowfish) or 256 bits (Twofish)
  • •Less common than AES

ChaCha20

  • •Stream cipher (not block cipher)
  • •256-bit key
  • •Fast on devices without hardware AES
  • •Used in TLS, WireGuard VPN

Asymmetric Algorithms

RSA

  • •Most widely used asymmetric algorithm
  • •Key sizes: 2048, 3072, 4096 bits
  • •2048 minimum, 4096 for high security
  • •Based on factoring large primes
  • •Used for encryption and signatures

ECC (Elliptic Curve Cryptography)

  • •Smaller keys for same security as RSA
  • •ECC-256 ≈ RSA-3072 in strength
  • •Faster and more efficient
  • •Used in ECDSA, ECDH

Diffie-Hellman (DH)

  • •Key exchange protocol
  • •Does NOT encrypt data directly
  • •Enables two parties to establish shared secret
  • •ECDH is elliptic curve version

Key Length Comparison

Security LevelSymmetricRSAECC
80-bit80-bit1024160
112-bit112-bit2048224
128-bit128-bit3072256
192-bit192-bit7680384
256-bit256-bit15360512

Key insight: RSA needs MUCH longer keys than AES for equivalent security. Don't compare key lengths across algorithm types directly.

Algorithm Status Overview

AlgorithmTypeStatusNotes
AESSymmetric✅ SecureCurrent standard
3DESSymmetric⚠️ DeprecatedPhase out
DESSymmetric❌ BrokenNever use
RSA-1024Asymmetric❌ WeakToo short
RSA-2048Asymmetric✅ MinimumAcceptable
RSA-4096Asymmetric✅ StrongHigh security
ECC-256Asymmetric✅ SecureEfficient
MD5Hash❌ BrokenNever use
SHA-1Hash⚠️ DeprecatedAvoid
SHA-256Hash✅ SecureCurrent standard

Block Ciphers vs. Stream Ciphers

Block Ciphers (AES, 3DES)

  • •Encrypt fixed-size blocks (e.g., 128 bits)
  • •Require padding for data not matching block size
  • •Different modes of operation (CBC, GCM, CTR)

Stream Ciphers (ChaCha20, RC4)

  • •Encrypt one bit/byte at a time
  • •No padding needed
  • •Generally faster for streaming data
  • •RC4 is broken—don't use

Quantum Computing Threat

Current asymmetric algorithms (RSA, ECC, DH) are vulnerable to quantum computers: • Shor's algorithm can break RSA and ECC • Post-quantum cryptography being developed • NIST standardizing quantum-resistant algorithms • AES-256 considered quantum-resistant for symmetric

How CompTIA Tests This

Example Analysis

Scenario: A company needs to choose encryption for a new file storage system. They need strong security that will remain secure for at least 10 years. What algorithm and key length should they use?

Recommendation: AES-256

Why AES: • Current standard, widely supported • Extremely fast with hardware acceleration • No known practical attacks

Why 256-bit: • Maximum AES key size • Quantum-resistant for symmetric encryption • 10+ year security requirement needs margin

Why NOT 3DES: • Deprecated, being phased out • Slower than AES • Block size limitations (64-bit blocks)

Why NOT RSA for bulk encryption: • Too slow for file encryption • Use RSA for key exchange, AES for data

Key insight: For bulk data encryption, symmetric (AES) is always the answer. The question is key length—256-bit for long-term or high-security requirements.

Key Terms to Know

encryption algorithmskey lengthAESRSA3DESkey sizeencryption strengthcryptographic algorithmsECC

Common Mistakes to Avoid

Comparing key lengths across algorithm types—AES-128 is not weaker than RSA-2048. They're different algorithm types with different key length requirements.
Using deprecated algorithms—3DES, MD5, SHA-1, DES, and RC4 should not be used for new implementations.
Thinking longer keys are always better—longer keys mean slower operations. Choose appropriate length for the use case.
Forgetting quantum computing implications—RSA and ECC will be broken by quantum computers. Plan for post-quantum transition.

Exam Tips

AES is THE symmetric standard. Know key sizes: 128, 192, 256 bits.
RSA minimum is 2048 bits. 1024 is too weak. 4096 for high security.
ECC provides same security as RSA with smaller keys: ECC-256 ≈ RSA-3072.
3DES is deprecated. If you see it as an option, it's probably wrong for new implementations.
DES, MD5, SHA-1, RC4 are all broken or deprecated. Never use for security.

Memory Trick

"AES is ACE"

  • •AES is the Accepted Current Encryption standard
  • •Key Length Memory:
  • •AES: 128/192/256 (remember 256 for maximum)
  • •RSA: 2048 minimum (remember "2K is OK")
  • •ECC: 256 equivalent to RSA-3072
  • •Algorithm Status:
  • •AES, RSA-2048+, ECC, SHA-256 = SECURE
  • •3DES, SHA-1 = DEPRECATED
  • •DES, MD5, RC4 = DEAD
  • •The Block Size Difference:
  • •AES = 128-bit blocks
  • •3DES = 64-bit blocks (that's why it's weak)
  • •Quantum Threat Memory:
  • •Symmetric (AES-256) = Survives quantum
  • •Asymmetric (RSA, ECC) = Broken by quantum

Test Your Knowledge

Q1.Which symmetric encryption algorithm is the current recommended standard?

Q2.What is the minimum recommended key length for RSA encryption?

Q3.Why does ECC require smaller key sizes than RSA for equivalent security?

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