Key Takeaways
- Attacks like brute force, replay, and chosen ciphertext exploit encryption flaws.
- Incidents like Heartbleed and the Equifax breach show the dangers of weak encryption.
- Future quantum advances may break current encryption, requiring post-quantum solutions.
- Strong passwords, MFA, AES-256 encryption, and regular updates help defend against attacks.
Nearly all your online activities, including banking, work profiles and private messaging, depend on cryptography for security. This is why your email password, online shopping details, and internet browsing history aren’t accessible to just anyone. But this digital security isn’t invincible. Cybercriminals have become creative, devising ways to bypass these defenses – a threat known as cryptographic attacks.
These attacks target the systems that encode and protect data, attempting to crack the encryption or manipulate weaknesses in security protocols. Understanding these threats is key to defending against them.
So, what are the types of attacks in cryptography that you should know about? Let’s break down the most common examples.
9 Security Attacks in Cryptography Explained
Encryption protects sensitive information by transforming it into unreadable code. But no system is entirely foolproof. Cybercriminals use different tactics to break encryption, exposing data that should remain private. Some attacks rely on sheer computing power, while others exploit flaws in algorithms or weaknesses in how encryption is used.
Brute Force Attack
A brute-force attack involves systematically trying every possible key or password until the correct one is found. Imagine a safe with a 4-digit combination lock. A brute-force attack would try every combination from 0000 to 9999 until the safe opens. This attack’s effectiveness depends on the key’s length and complexity.
In February 2025, Honeypots detected a sharp rise in brute-force attacks on edge devices, many launched from malware-infected equipment. The Shadowserver Foundation reported up to 2.8 million unique IPs per day involved, with 1.1 million from Brazil.
Ciphertext-Only Attack
Not all attacks need a starting clue. In a ciphertext-only attack, the attacker only has access to the ciphertext and attempts to deduce the plaintext or the key. For example, if a cyber attacker intercepts encrypted emails, they might try to analyze the patterns in the ciphertext to find the original message without any other information.
This attack exploits weaknesses in the encryption algorithm or its implementation that reveal patterns in the ciphertext.
While modern encryption makes this attack much harder, it’s not impossible. In 2003, researchers Barkan, Biham, and Keller successfully launched a ciphertext-only attack against encrypted GSM phone calls, demonstrating that even widely used encryption systems can have vulnerabilities.
Known-Plaintext Attack
In a known-plaintext attack, hackers access an encrypted message and its original, unencrypted version. By studying how the plaintext transforms into ciphertext, they attempt to reverse-engineer the encryption process or uncover the key.
During World War II, the Allies determined daily key settings using captured Enigma machines and known plaintexts, such as weather reports.
Chosen-Plaintext Attack
A chosen-plaintext attack is like testing a secret code by feeding it different messages and studying the results. The attacker picks specific text, runs it through the encryption system, and carefully examines the scrambled output. Over time, patterns appear, revealing weaknesses in how the system hides information. This method can help crack the encryption or expose the key that protects data.
Attempting to reverse-engineer an encryption algorithm could involve a chosen-plaintext attack, where an attacker encrypts controlled inputs (e.g., ‘AAAAAA’ → ‘X3HGT9’, ‘BBBBBB’ → …) to observe corresponding ciphertexts. This iterative approach allows them to map input-output relationships, deducting the encryption’s secrets and breaking its security.
Chosen-Ciphertext Attack
A chosen-ciphertext attack (CCA) is the reverse of a chosen-plaintext attack. It lets the hacker analyze chosen ciphertexts and their plaintexts to obtain a secret key or system information. Unlike chosen-plaintext attacks, CCA manipulates ciphertexts, often by tricking someone with the key into decrypting arbitrary blocks. Attackers submit nonsense ciphertexts and observe the results or modify existing ciphertexts to find the key. This is effective against public-key systems like early RSA.
The vulnerability is information leakage during decryption via errors, timing, or outputs. Systems allowing arbitrary ciphertext submissions are susceptible. An adaptive CCA (CCA2) involves adaptively chosen ciphertexts, crucial for security analysis. A non-adaptive CCA (CCA1) lacks this adaptive querying. CCA reverses the decryption process by observing manipulated inputs and outputs, targeting systems revealing decryption information.
Key and Algorithm Attack
Key and algorithm attacks exploit inherent weaknesses within the encryption algorithm itself. Success means compromising all data protected by that system. Attackers analyze the algorithm for mathematical flaws, predictable structures in key generation, or implementation errors like incorrect padding. This allows them to bypass traditional decryption methods.
The exploited vulnerability lies in algorithms based on weak mathematical foundations, poor randomness, or outdated principles. Predictable patterns enable attackers to develop specialized cracking tools.
An example is the MD5 hashing algorithm. Once widely used, researchers discovered its vulnerability to collision attacks. These collisions, where different inputs produce the same hash, can be found within seconds and used maliciously.
In 2012, the Flame spyware, which infiltrated thousands of computers in Iran, exploited MD5 collisions to generate counterfeit Microsoft update certificates. This allowed the spyware to authenticate critical systems, highlighting the severe compromise of MD5’s security.
Side-Channel Attack
Side-channel attacks bypass mathematical encryption breaking by targeting physical signals emitted during cryptographic processes. Attackers analyze power consumption, electromagnetic radiation, timing, or acoustic emissions to extract encryption key information.
By placing sensors near devices performing cryptographic operations, attackers can detect patterns in these signals that reveal bits of the key. This exploits vulnerabilities in systems that unintentionally leak information through physical signals. Researchers have demonstrated this by extracting 256-bit keys from hardware wallets via power analysis, highlighting cryptocurrency storage risks.
Replay Attack
Some attacks don’t require breaking encryption at all. Instead, hackers capture and reuse previously sent data to deceive a system. In a replay attack, an attacker records a valid data transmission and sends it again later to gain unauthorized access.
Consider a scenario where a cybercriminal intercepts the wireless data exchanged during a contactless payment. Instead of physically taking someone’s payment card, they digitally capture the transaction details transmitted between the card and the payment device. Subsequently, they could attempt to replay this recorded transaction at a different merchant, aiming to complete a purchase fraudulently.
Early Wi-Fi security protocols (WEP) were highly vulnerable to replay attacks. Hackers could capture authentication messages exchanged between a device and a Wi-Fi router and then resend them to gain unauthorized access to the network. This flaw contributed to the downfall of WEP security and the adoption of more secure protocols like WPA2.
Dictionary Attack
A dictionary attack is a targeted version of a brute force attack. Instead of trying every possible combination of characters, hackers use pre-compiled lists of the most commonly used passwords to crack accounts faster. This method is highly effective because many people still rely on simple, predictable passwords.
Instead of generating random letter and number combinations, a hacker begins with high-probability passwords like “password,” “123456,” “qwerty,” and other common phrases leaked in past data breaches. By automating this process, attackers can quickly test thousands or even millions of likely passwords in seconds.
The RockYou breach in 2009 exposed over 32 million plaintext passwords from a hacked database. Cybercriminals used dictionary attacks to crack and leak these passwords, many of which were as simple as “123456.”
Biggest Cryptography Attacks
Even robust encryption can fail when attackers exploit weaknesses. Here are some major examples:
WannaCry Ransomware (2017):
WannaCry was a global ransomware attack in May 2017 that exploited the “EternalBlue” vulnerability in older Windows SMB protocol versions. Once a system was infected, it encrypted files using AES and RSA, demanding Bitcoin for decryption. Its worm-like nature enabled rapid self-propagation across networks. The attack hit 200,000 devices across 150 countries, leading to losses of between $4 billion and $8 billion, and severely impacting healthcare, transportation, banking, and telecom. The UK’s NHS was paralyzed, canceling thousands of appointments.
Equifax Data Breach (2017):
In 2017, Equifax, a major U.S. credit reporting agency, experienced a massive data breach affecting approximately 147 million individuals. Sensitive personal information was exposed, including Social Security numbers, birth dates, addresses, and, in some cases, driver’s license and credit card details. The breach resulted from exploiting a known, unpatched vulnerability in the Apache Struts web server software, allowing attackers to access and exfiltrate vast amounts of data over several months.
Yahoo Hacks (2013 & 2014):
Yahoo disclosed two significant data breaches in 2013 and 2014, impacting billions of user accounts worldwide. The 2013 breach compromised all three billion accounts, and the 2014 breach affected 500 million. Stolen information included names, email addresses, phone numbers, dates of birth, hashed passwords, and security questions and answers. Attributed to state-sponsored actors, the attacks involved gaining deep network access, with the 2014 breach involving the theft of code to forge authentication cookies. The password hashing was also found to be weak.
How to Prevent Cryptographic Attacks
Strengthening your defenses against cryptographic attacks requires proactive steps:
- Use strong, complex passwords and enable multi-factor authentication.
- Regularly update software to patch vulnerabilities.
- Encrypt sensitive data using trusted, modern algorithms like AES-256.
- Employ security protocols like TLS to safeguard data in transit.
- Limit user permissions to reduce potential entry points for attackers.
- Implement secure session tokens to prevent replay attacks.
- Regularly audit your systems for potential weaknesses.
What is Q Day? Quantum Cryptography Attacks Explained
Quantum computing has the potential to break traditional encryption methods by performing calculations far faster than current systems allow. Q Day refers to the point when quantum computers become powerful enough to render much of today’s encryption obsolete.
Researchers are developing post-quantum cryptography – encryption systems designed to resist quantum attacks to prepare for this shift. While Q Day is still a future concern, businesses are already exploring these new standards to stay ahead.
Closing Thoughts
Digital security is an ongoing process, not a one-time fix. It involves protecting data through cryptographic techniques, user authentication, system updates, and strict protocols. Each new defense method invites innovation and fresh challenges, urging security specialists to carefully weigh improvements against emerging vulnerabilities. In the end, the effort to protect user information is a continuous dialogue between advancing technology and the inventive strategies of those seeking to breach it.
