What are the types of attacks in encryption?

Encryption is used to protect sensitive information and provide security for data transmission and storage. However, various types of attacks can be used to try and break encryption schemes. Understanding the different types of attacks is important for improving encryption algorithms and properly securing systems.

Table of Contents

What are the main goals of attacks against encryption?

The main goals of attacks against encryption algorithms and implementations are:

Obtain the secret encryption key – With the key, an attacker can easily decrypt any data protected by the algorithm.

Break the cipher – Determine the encryption algorithm to decrypt data without the secret key.
Introduce weaknesses – Modify encryption algorithms or implementations to make the system vulnerable.
Access plaintext – Obtain decrypted data through cryptanalysis or by exploiting weaknesses in implementations.

Cause denial-of-service – Prevent authorized users from accessing encrypted data.

What are brute force attacks?

Brute force attacks involve trying every possible key or password to break the encryption. As key lengths increase, the number of potential keys rises exponentially, making brute force infeasible. However, weaknesses in key generation or storage may make brute forcing easier. Brute force attacks are typically performed by specialized software running through all possible combinations.

Brute force attack steps

Obtain encrypted data

Try decrypting with each possible key
Check if output is coherent
Repeat until correct key is found

Defending against brute force attacks

Use long encryption keys – Increases number of combinations
Add delays between attempts – Slows brute forcing
Lockout after failed attempts – Stops automated attacks

Use salts and iterations for key derivation – Increases compute time

What are side-channel attacks?

Side-channel attacks extract secrets or compromise devices by analyzing indirect outputs and physical characteristics such as:

Timing – Measure encryption time to infer algorithm steps or key bits

Power consumption – Use power usage patterns to find keys
Electromagnetic emissions – Capture stray radio signals to find secrets
Sound – Use acoustic analysis to extract sensitive data

Defending against side-channel attacks

Constant execution time – Avoid variations that leak information
Power masking and filtering – Hide power consumption patterns
Protected execution environments – Reduce available signals

Tamper-resistant hardware – Prevent physical access to devices

What are known plaintext attacks?

Known plaintext attacks use pairs of plaintext and matching encrypted text to analyze and find weaknesses in encryption algorithms or keys. The pairs provide insights into how the plaintext is transformed during encryption. Some examples include:

Ciphertext-only attack – Attacker only has ciphertext

Known plaintext attack – Attacker has ciphertext and matching plaintext
Chosen plaintext attack – Attacker can choose arbitrary plaintext to be encrypted

Defending against known plaintext attacks

Use strong ciphers not vulnerable to analysis

Frequently change encryption keys
Add randomness to plaintext before encryption
Encrypt multiple plaintexts with same key

What are man-in-the-middle attacks?

In man-in-the-middle (MITM) attacks, the attacker secretly sits between two communicating parties to eavesdrop and tamper with the communication. The attacker can intercept and modify data flowing between the two victims.

Man-in-the-middle attack steps

Attacker situates between two victims
Impersonates each victim to the other

Views and modifies intercepted traffic
Forwards modified data to original recipients

Defending against man-in-the-middle attacks

Encrypt communication to prevent eavesdropping

Check digital signatures to prevent tampering
Pin public keys to entity identities
Use trusted certificates to authenticate connections

What are replay attacks?

In a replay attack, valid data transmission is maliciously repeated or delayed. The attacker eavesdrops and records communication then replays it later to produce unauthorized effects. For example, intercepting a funds transfer transaction and resending it multiple times to steal money.

Replay attack steps

Attacker intercepts valid data
Communication session ends

Attacker resends data
System processes data again

Defending against replay attacks

Use timestamping and limited validity periods

Sequence numbers and nonces to detect duplicates
One-time encryption keys
Authentication and integrity checks on data

What are birthday attacks?

Birthday attacks exploit the mathematics behind hash functions to find collisions where different inputs produce the same hash output. This can be used to falsify data and bypass integrity checks that use cryptographic hashes.

Birthday attack steps

Attacker gathers or precomputes large number of message hashes
Finds two messages with the same hash through analysis

Substitutes one message for the other to fool integrity checks

Defending against birthday attacks

Use larger hash output sizes – Increases number of possible values
Introduce randomness – Lowers chances of collisions

Add secret salts – Requires attacker to match salted hashes

What are rainbow table attacks?

Rainbow tables are precomputed lookup tables used to quickly reverse cryptographic hash functions. Instead of brute forcing hashes, attackers search for them in a rainbow table to find plaintext passwords.

Rainbow table creation

Generate password hashes with different salts

Partially invert hashes to create chains ending in plaintext
Store start and end points of chains in a table

Defending against rainbow table attacks

Use salt – Requires attacker to match salted hash

Use key stretching – Increases compute time to generate chains
Memory-hard hashing – Makes tables generation expensive

What are dictionary attacks?

Dictionary attacks try common passwords and words to break encryption keys and passwords. Lists of common passwords and wordlists are used sequentially or in combination until the correct key is found.

Defending against dictionary attacks

Use strong passwords – Makes guessing harder
Salts – Requires attacker to match full salted hashes
Slow hashing – Increases time to hash each word

Lock accounts after failed attempts

What are chosen ciphertext attacks?

In chosen ciphertext attacks, the attacker can provide arbitrary ciphertexts to be decrypted and observe the results. This allows analysis of encryption algorithms and inferring key information based on error messages and decrypted plaintexts.

Chosen ciphertext attack types

CPA – Chosen plaintext attack

CCA1 – Attacker submits ciphertexts before obtaining secret key
CCA2 – Attacker submits ciphertexts before and after obtaining key

Defending against chosen ciphertext attacks

Decryption integrity checks

Careful error handling to avoid leaking information
Use encryption modes secure against CCA like AES-GCM

Comparison of Attack Types

Here is a comparison of some common encryption attack types:

Attack Type	Goal	Knowledge	Resources Needed
Brute force	Find secret key	Ciphertext	High computational power
Known plaintext	Determine algorithm	Plaintext-ciphertext pairs	Moderate time and bandwidth
Birthday	Find hash collisions	Hash function	Large number of known hashes
Side-channel	Extract key information	Access to encryption device	Specific measurement tools
MITM	Intercept communication	Access to transmitted data	Proximity to victims

How can attacks be combined for more impact?

Attackers can combine multiple techniques to build more sophisticated and effective attacks:

Use side-channel leaks to reduce brute force search space
Analyze known plaintext pairs then perform MITM attack with chosen ciphertexts

Brute force password hashes retrieved through rainbow table lookup
Test chosen plaintexts after exploiting implementation flaws

Layered defenses are needed to protect against combined attacks targeting different aspects of an encryption system. The strongest defense is using robust encryption algorithms and properly implementing systems without flaws that leave them vulnerable.

How can encryption be weakened by modifying algorithms or protocols?

Encryption algorithms and protocols can be weakened in various ways to make them easier to break. Some examples include:

Reduce key sizes – Makes brute forcing faster
Remove key derivation steps – Weakens entropy and may reuse keys

Use non-random initialization vectors – Introduces patterns in output
Reuse keys across messages – Allows attacks on multiple messages
Reduce number of algorithm rounds – Speeds analysis of cipher structure

Allow unauthenticated modes – Enables malleability attacks

Even small changes can significantly degrade security. Cryptography should be implemented using well-tested reference algorithms and following industry best practices to avoid weaknesses.

Conclusion

There are many types of attacks that target the implementation and algorithms behind encryption systems. Understanding common attacks like brute force, side-channel, MITM, and rainbow tables helps developers properly secure systems and defend against compromises of encrypted data. Carefully implementing cryptosystems using strong, standard algorithms can prevent many attacks.

Ongoing research in cryptography produces new attack techniques as well as improved defenses. Keeping encryption systems updated and properly configured provides the best protection against current and emerging threats targeting sensitive encrypted data.