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An encryption key is a cryptographic value used with an algorithm to protect information. What the term means depends on the method: symmetric encryption uses a shared secret key, while public-key encryption uses a public key paired with a private key. The public key is not secret; the corresponding private key is.
What are encryption keys?
A cryptographic key is a value or parameter that controls a cryptographic operation. Depending on its purpose, a key may be used to encrypt or decrypt information, create or verify a digital signature, authenticate a party, or protect another key. “Encryption key” is therefore best understood in context rather than as a name for every key in a cryptographic system.
NIST’s glossary definition of an encryption key distinguishes the term by method: in symmetric encryption, it is the symmetric key; in public-key encryption, it is the public key in the pair.
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How do symmetric and public-key encryption keys differ?
| Feature | Symmetric encryption | Public-key encryption |
|---|---|---|
| Key structure | One shared secret key | A public key and a corresponding private key |
| Encryption and paired operation | The same key supports encryption and its inverse, such as decryption. | The public key can encrypt; the corresponding private key supports decryption in that encryption scheme. |
| What must remain secret? | The symmetric key must not be disclosed to unauthorized parties. | The private key must be protected. The public key is meant to be shared. |
| Important context | The key is shared among authorized users or systems that need to perform the operation. | Public/private pairs can support different roles, including encryption, key establishment, signing, or authentication; identify the role rather than treating all uses as interchangeable. |
NIST defines a symmetric key as the key used for an operation and its inverse, such as encryption and decryption. In public-key encryption, the term “encryption key” refers to the public key—not the private key. The private key is protected and used for its corresponding role.
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How are cryptographic keys classified by purpose?
Key classifications also describe what a key does, not just whether a system uses one key or a pair. NIST SP 800-57 Part 1 Revision 5 discusses several roles:
- Data-encryption keys: protect data confidentiality.
- Signature-generation keys: create digital signatures.
- Signature-verification keys: verify digital signatures.
- Authentication keys: support authentication.
- Key-wrapping keys: protect other keys.
A key’s role determines the protection it needs. For example, a public verification key can be distributed, whereas a private signing key must be protected against unauthorized use.
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What does key management involve?
Key management covers selecting, protecting, using, and replacing cryptographic keying material. NIST SP 800-57 Part 1 Revision 5 provides general guidance and best practices for key types, protection, and management functions. NIST lists it as published May 4, 2020; consult NIST’s publication page for any newer revision before relying on it as current implementation guidance.
For an organization, the key-management question is not only “Which key encrypts this?” It is also who is authorized to access each key, what operation it supports, how it is protected during use and storage, and how it is replaced when necessary. The appropriate controls depend on the key’s type and role; symmetric and asymmetric approaches should not be treated as universally safer or better than one another.
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See NIST SP 800-57 Part 1 Revision 5 for the publication record and the standard’s key-management guidance.
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- BUILT TO LAST: Made from tough, waterproof, and crush-resistant materials. Manufactured in Sweden and programmed in the USA with the highest security standards.
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