keywrapping

Key wrapping is a cryptographic technique used to securely encapsulate key material by encrypting it with another key, called the key-encryption key (KEK). The result is a wrapped key blob that preserves confidentiality and, in well-designed schemes, integrity during storage or transmission. The typical goal is to protect keys used for data encryption, authentication, or other cryptographic operations from disclosure or tampering.

In a standard key-wrap process, a KEK is applied to a content-encryption key or other sensitive material (the CEK or key material). The wrapping algorithm produces a structured, opaque blob that can be stored or sent. When needed, a corresponding unwrap operation uses the same KEK to recover the original key material. Good key wrapping schemes provide both confidentiality and tamper detection, so altered wrapped keys are detected during unwrap.

Common standards and algorithms include AES Key Wrap (RFC 3394) and AES Key Wrap with Padding (RFC 5649). These specify how the KEK and the wrapped key are combined, including any initialization data and integrity checks. National and industry guidelines, such as NIST SP 800-38F, describe recommended practices for using key wrap in key management. While AES KW is the most widely used, other methods exist, including public-key-based wrapping (for example RSAES-OAEP) in hybrid schemes and CMS-specific wrap formats.

Applications include securing keys at rest, protecting keys during transport between systems or components, and safeguarding backups. Key management practices—proper generation and protection of KEKs, regular rotation, access controls, and secure storage in hardware security modules—are essential to the security of a key-wrapping solution.