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Secret-key cryptography—also called symmetric-key cryptography—uses a shared secret key to perform a cryptographic operation and its complement. For encryption, authorized parties use the same key to encrypt and decrypt information. They must protect that key from disclosure.
What is a secret key?
A cryptographic key is a value used with an algorithm to determine how it operates. In secret-key cryptography, authorized parties share secret key material. “Secret” means the key must be protected from disclosure; it is not a classification level. NIST’s glossary definition of secret key explains the terminology.
The key is distinct from the algorithm. The key is the parameter supplied to the algorithm; AES, for example, is an algorithm. If someone obtains a key, they may be able to carry out the same key-dependent operation or reverse an encrypted operation. That is why safeguarding the key is central to the system.
How does secret-key encryption work?
For encryption, the sender and recipient use the same secret key: one applies it with an encryption algorithm to turn readable information into ciphertext, and the other applies it with the corresponding decryption operation to recover the information. The key is shared only with authorized parties, not made public.
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Secret-key algorithms are not limited to encryption and decryption. Depending on the algorithm and its purpose, a key can also be used for operations such as keyed hashing or message authentication. NIST describes these broader uses in its symmetric-key algorithm glossary entry.
Secret-key vs. public-key cryptography
The central distinction is how the keys relate. Symmetric cryptography uses the same secret key for an operation and its complement. Public-key cryptography uses separate, related keys. In a key-establishment scenario, public-key methods can let parties communicate without having previously shared a secret key; this is a narrower distinction, not a claim that public-key methods remove every role for symmetric keys.
| Aspect | Secret-key (symmetric) | Public-key |
|---|---|---|
| Key relationship | The same secret key is used for the operation and its complement. | Separate, related keys are used. |
| Prior shared secret | Authorized parties need access to the shared secret key for the operation. | Key establishment can allow parties to communicate without prior access to a shared secret. |
This is a basic conceptual comparison; real communication protocols can combine cryptographic techniques. NIST outlines the key-establishment distinction in its public-key cryptography glossary entry.
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1Scan for outdated or missing drivers - takes under a minute2Clear out junk files and repair common Windows errors3Fix the driver behind crashes, sound loss and screen glitchesIs AES secret-key cryptography?
Yes. AES, or the Advanced Encryption Standard, is a symmetric block cipher that can encrypt and decrypt information. AES is the algorithm; the secret key is the value used with it. NIST published FIPS 197, the AES standard, on November 26, 2001. That publication date alone does not establish the standard’s current revision status. See NIST FIPS 197.
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What to remember
- “Secret-key” and “symmetric-key” describe the same basic cryptographic approach.
- For encryption, authorized parties share the same key for encryption and decryption.
- The key is a parameter used with an algorithm, not the algorithm itself.
- Because possession of the key can enable key-dependent operations, protecting it from disclosure matters.
- Public-key cryptography instead uses separate related keys, and key establishment can work without a previously shared secret.
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