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1Clear out junk files and repair common Windows errors2Fix the driver behind crashes, sound loss and screen glitches3Repair Windows errors before they cause bigger problemsSecret-key cryptography, also called symmetric-key cryptography, uses a shared secret key for a cryptographic operation and its complement. For encryption, authorized parties use the same key to encrypt and decrypt information. The key must be protected from disclosure; “secret” here describes that protection requirement, not a security-classification level.
What is secret-key cryptography?
It is a cryptographic approach in which authorized parties share secret key material. A cryptographic key is a parameter used with an algorithm to determine how the algorithm operates. In encryption, the shared key lets an authorized party encrypt information and another authorized party decrypt it.
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The key and the algorithm are different things: the key is the value supplied to an algorithm, while the algorithm defines the cryptographic method. Because authorized parties share the key, someone who obtains it may be able to perform the same key-dependent operation or reverse an encrypted operation. NIST defines a cryptographic key and describes the symmetric-key concept.
What is a secret key used for?
Encryption and decryption are a familiar example, but symmetric-key algorithms can also be used for other operations, including keyed hashing and message authentication. The exact purpose depends on the algorithm and how it is used; “secret key” does not mean the key is exclusively for encryption.
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Whatever the operation, the key must not be made public. NIST uses “secret” to indicate the need to protect the key from disclosure, not to assign it a classification level. See NIST’s definition of secret key and its entry on symmetric cryptography.
Example: AES
AES, or the Advanced Encryption Standard, is a well-known symmetric block cipher that can encrypt and decrypt information. AES is the algorithm, not the secret key itself. NIST published FIPS 197, the AES standard, on November 26, 2001; that publication date alone does not establish the standard’s current revision status. NIST’s FIPS 197 publication provides the standard.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Secret-key vs. public-key cryptography
The basic distinction is whether the relevant cryptographic operation relies on the same shared secret key or on separate related keys. This is a conceptual comparison, not a full description of how every real-world protocol combines cryptographic methods.
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| Feature | Secret-key (symmetric-key) cryptography | Public-key cryptography |
|---|---|---|
| Key arrangement | Authorized parties share secret key material; the same key is used for an operation and its complement, such as encryption and decryption. | Uses separate, related keys. |
| Prior shared secret | For the shared-key operation, the authorized parties need access to the secret key. | NIST describes public-key key establishment as allowing parties to communicate without prior access to a shared secret key. |
That public-key key-establishment capability does not mean symmetric keys are never needed. It addresses whether parties must already have a shared secret for that key-establishment scenario. NIST’s public-key cryptography entry explains the separate-key approach.
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What to remember
- “Secret-key” and “symmetric-key” are equivalent terms in this context.
- The shared key is a parameter used with an algorithm; it is not the algorithm itself.
- For encryption, the same secret key is used to encrypt and decrypt.
- AES is an example of a symmetric block cipher.
- Public-key cryptography uses separate related keys and can support key establishment without a previously shared secret.
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