What is Cryptography in security? What are the different types of Cryptography?

Cryptography is the science of securing information so that only authorized parties can read or use it. It uses mathematical techniques to protect data against outside observers, and it comes in three main forms: symmetric (secret key) cryptography, asymmetric (public key) cryptography, and hash functions.

Cryptography is the practice of protecting information using mathematical techniques so that only authorized parties can access it. It secures communication and data against outside observers, and underpins encryption, digital signatures, and secure authentication. Cryptography has three main types: symmetric (secret key) cryptography, asymmetric (public key) cryptography, and hash functions. Together they provide confidentiality, integrity, authentication, and non-repudiation.

Key Takeaways

• Cryptography is the science of securing information with mathematical techniques so only authorized parties can read or use it.
• It has three main types: symmetric (one shared secret key), asymmetric (a public and private key pair), and hash functions (one-way, irreversible).
• Cryptography pursues four objectives: confidentiality, integrity, authentication, and non-repudiation.
• Encryption is one application of cryptography. Cryptography is the broader field that also includes hashing, digital signatures, and key exchange.
• Older algorithms such as DES, MD5, and SHA-1 are broken or deprecated. Modern cryptography uses AES, SHA-2 or SHA-3, and is beginning to adopt post-quantum algorithms.

What Is Cryptography?

Cryptography is the study and practice of securing communication and data from outside observers. It works by transforming readable information (plaintext) into an unreadable form (ciphertext) using an algorithm and a key. Only someone with the correct key can reverse the transformation and recover the original information.

The strength of a cryptographic system depends on the quality of its algorithms and the randomness and secrecy of its keys, which is what makes the key hard to guess and the system hard to break.

It is worth distinguishing cryptography from encryption. Encryption, the reversible scrambling of data, is one application of cryptography. Cryptography is the broader discipline that also covers hashing (one-way transformations), digital signatures, and secure key exchange. Encryption is a tool; cryptography is the field.

The Four Objectives of Cryptography

Cryptography is designed to achieve four security objectives. Different techniques deliver different combinations of them.

• Confidentiality: Only the intended recipient can read the information. Anyone else sees only ciphertext.
• Integrity: The information cannot be altered in storage or transit without detection.
• Authentication: The sender and recipient can verify each other’s identity and the origin of the data.
• Non-repudiation: A sender cannot later deny having sent a message, which is essential for contracts and financial transactions.

A Brief History of Cryptography

Cryptography began with simple ciphers, the earliest well-known example being the Caesar cipher, which shifted each letter of a message by a fixed number of positions. Early ciphers used keys and plaintext just as modern systems do, but they were far easier to break. Over time, as the need to protect data grew and old ciphers were broken, cryptography advanced to the complex mathematical algorithms used today, some of which would take current computers many years to break, and some of which (hash functions) are deliberately irreversible.

Types of Ciphers

A cipher is an algorithm for performing encryption and decryption. Ciphers can be categorized by how they transform data:

• Substitution cipher: Each unit of plaintext is replaced with another, as in the Caesar cipher.
• Transposition cipher: The positions of the units are rearranged according to a system.
• Stream cipher: Data is encrypted one bit or byte at a time using a keystream.
• Block cipher: Data is encrypted in fixed-size blocks, as AES does.
• Public key cipher: A pair of mathematically related keys is used, one to encrypt and one to decrypt.

The Three Main Types of Cryptography

Modern cryptography is generally divided into three categories, each serving different purposes.

Type	How it works	Common algorithms
Symmetric (secret key)	One shared key encrypts and decrypts. Fast; ideal for bulk data.	AES; DES (deprecated); 3DES (deprecated)
Asymmetric (public key)	A public and private key pair; one encrypts, the other decrypts.	RSA, ECC, Diffie-Hellman
Hash functions	One-way, irreversible transformation to a fixed-length value.	SHA-2, SHA-3; MD5 and SHA-1 (broken)

1. Symmetric (Secret Key) Cryptography

Symmetric cryptography uses a single shared key for both encryption and decryption. It is the fastest form of cryptography, which makes it ideal for encrypting large amounts of data. Its challenge is that the shared key must be delivered securely to both parties, so it is often used for data at rest, or combined with asymmetric cryptography for data in transit. The leading algorithm is AES; DES is deprecated. See EC’s explainer on symmetric encryption for detail.

2. Asymmetric (Public Key) Cryptography

Asymmetric cryptography uses two mathematically related keys: a public key that can be shared freely, and a private key that is kept secret. Data encrypted with one key can only be decrypted with the other. Crucially, the private key cannot be feasibly derived from the public key, which is what makes it safe to publish the public key. This solves the key distribution problem that limits symmetric cryptography, and it enables digital signatures. Common algorithms include RSA, elliptic-curve cryptography (ECC), and Diffie-Hellman.

3. Hash Functions

A hash function is a one-way, irreversible transformation that turns an input of any size into a fixed-length output called a hash. A good hash function produces a unique output for each input, and the only way to reverse it is to try every possible input. Because they are irreversible, hashes are used to protect passwords and to verify data integrity, and they are a building block of digital signatures and certificates. Secure options today are the SHA-2 family (SHA-256, SHA-384, SHA-512) and SHA-3. Older functions such as MD5 and SHA-1 are broken and should not be used for security purposes.

Cryptography and the Post-Quantum Transition

Cryptography is undergoing its biggest change in decades. A sufficiently powerful quantum computer running Shor’s algorithm could break today’s asymmetric cryptography (RSA, ECC, Diffie-Hellman), which protects key exchange and digital signatures. In response, NIST standardized post-quantum algorithms in August 2024, including ML-KEM (FIPS 203) for key establishment and ML-DSA (FIPS 204) for signatures. Symmetric cryptography and hash functions are far less affected: AES-256 and SHA-384 or higher remain secure. See EC’s post-quantum cryptography resources for how the migration works.

How Encryption Consulting Helps

Understanding the types of cryptography is the starting point; applying them correctly across an organization is the hard part. Encryption Consulting’s Encryption Advisory Services help organizations choose the right cryptographic techniques for each use case, design an architecture aligned to NIST and FIPS guidance, and put sound key management in place, including HSM-backed key storage. As algorithms evolve toward post-quantum standards, we also help build the crypto-agility to adapt without re-engineering. Backed by ISO/IEC 27001:2022 and SOC 2 certified practices.

Frequently Asked Questions

What is cryptography in simple terms?

Cryptography is the science of protecting information using mathematical techniques, so that only authorized people can read or use it. It scrambles readable data into an unreadable form that can only be turned back with the correct key. Cryptography secures things like private messages, online payments, and stored files, and it also lets us verify who sent something and confirm that data has not been tampered with.

What are the three main types of cryptography?

The three main types are symmetric cryptography, asymmetric cryptography, and hash functions. Symmetric (secret key) cryptography uses one shared key to encrypt and decrypt and is fast. Asymmetric (public key) cryptography uses a public and private key pair and solves the problem of sharing keys securely. Hash functions are one-way, irreversible transformations used to protect passwords and verify data integrity. Most systems use a combination of all three.

What is the difference between cryptography and encryption?

Cryptography is the broad field of securing information with mathematical techniques. Encryption is one application within that field: the reversible process of scrambling data so it can later be unscrambled with a key. Cryptography also includes hashing (one-way transformations), digital signatures, and secure key exchange. In short, encryption is a specific tool, and cryptography is the wider discipline that contains it.

What are the four objectives of cryptography?

The four objectives are confidentiality, integrity, authentication, and non-repudiation. Confidentiality keeps data secret from anyone without the key. Integrity ensures data has not been altered. Authentication verifies the identity of the sender and recipient. Non-repudiation prevents a sender from later denying they sent a message. Different cryptographic techniques provide different combinations of these four goals.

What is a hash function used for?

A hash function turns an input of any size into a fixed-length output and is irreversible, meaning you cannot recover the original input from the hash. This makes hashes ideal for storing passwords (the system stores the hash, not the password), verifying that data has not changed (any change produces a different hash), and building digital signatures and certificates. Secure hash functions today include the SHA-2 family and SHA-3.

Which cryptographic algorithms are still considered secure?

For symmetric encryption, AES (especially AES-256) is the standard. For hashing, the SHA-2 family (SHA-256, SHA-384, SHA-512) and SHA-3 are secure. For asymmetric cryptography, RSA and ECC remain secure against classical computers but are threatened by future quantum computers, which is why NIST has standardized post-quantum algorithms like ML-KEM and ML-DSA. Avoid DES, 3DES, MD5, and SHA-1, which are broken or deprecated.

Apply the Right Cryptography for Your Needs

Knowing the types of cryptography is one thing; deploying them securely with sound key management is another. Explore Encryption Consulting’s Encryption Advisory Services to design and strengthen a cryptographic strategy aligned to NIST and FIPS guidance.