Skip to main content
DataRidge
Category: Cryptography and Encryption

Asymmetric Encryption

Also known as: Public-Key Cryptography, Asymmetric Cryptography
Simply put

Asymmetric encryption is a method of protecting data that uses two mathematically related keys instead of one: a public key that can be shared openly and a private key that is kept secret. Typically, data encrypted with one key can only be decrypted with the other, so information encrypted with someone's public key can be read only by the holder of the matching private key. This approach also underpins digital signatures, where the private key signs and the public key verifies.

Formal definition

Asymmetric encryption, also referred to as public-key cryptography, is a cryptographic scheme that uses a mathematically linked key pair, a public key and a private key, to perform complementary operations. One key encrypts data or generates a digital signature, while the corresponding key decrypts the data or verifies the signature. The public key may be distributed freely while the private key must remain confidential; the security model depends on the computational difficulty of deriving the private key from the public key. This entry defines the mechanism only and does not address specific algorithms, key lengths, key management practices, or implementation choices, and it does not cover how such controls map to any particular regulatory obligation. As a security control, encryption is distinct from data governance concerns; note also that encrypting personal data generally does not render it non-personal, since the data typically remains recoverable and the encryption is reversible with the appropriate key.

Why it matters

Asymmetric encryption underpins much of the secure communication and identity verification that data protection programs rely on, from protecting data in transit to enabling digital signatures. Its two-key model solves a problem that symmetric encryption cannot address on its own: parties can exchange information securely without first sharing a secret key, because the public key can be distributed openly while the private key stays confidential. This capability supports both confidentiality and, through digital signatures, integrity and authenticity assurances.

For privacy and security professionals, it is important to keep asymmetric encryption in its proper place as a security control rather than a governance or compliance solution. Encryption is a technical safeguard concerned with confidentiality; it does not by itself establish data ownership, lineage, lawful basis, or retention practices, which fall under data governance and the applicable legal regime. A common expert-level error is to assume that encrypting personal data removes it from regulatory scope. Encryption is generally reversible with the appropriate key, so encrypted personal data typically remains personal data and continues to attract the associated obligations.

Because this entry defines the mechanism only, it does not assess whether deploying asymmetric encryption satisfies any particular obligation. Whether a given implementation is adequate depends on context, including algorithm choice, key length, key management, and how the control maps to the specific requirements of the applicable framework, none of which are within the scope of this definition.

Who it's relevant to

Privacy Engineers and Security Architects
Those designing systems that protect data in transit or at rest, or that rely on digital signatures for authenticity, need to understand the two-key model and its dependence on private key confidentiality. They should treat algorithm, key length, and key management as separate implementation decisions beyond the scope of the mechanism itself.
Data Protection Officers and Compliance Officers
DPOs and compliance staff should recognize asymmetric encryption as a security control that can support safeguarding obligations, while avoiding the assumption that encryption alone satisfies any specific requirement or removes data from regulatory scope. Because the encryption is generally reversible with the private key, encrypted personal data typically remains personal data.
Information Governance Leads
Governance leads should keep encryption, a confidentiality control, distinct from governance concerns such as ownership, stewardship, data quality, and lineage. The two overlap where security controls support data protection policy, but encryption does not substitute for governance functions.

Inside Asymmetric Encryption

Public and Private Key Pair
Asymmetric encryption relies on two mathematically related keys: a public key that can be shared openly and a private key that must be kept secret by its holder. Data encrypted with one key can generally only be decrypted with its counterpart.
Public Key
The freely distributable key typically used to encrypt data intended for the key owner, or to verify a digital signature the owner produced. Its exposure does not, on its own, compromise the confidentiality of the encrypted data.
Private Key
The secret key that must remain under the sole control of its holder. Its confidentiality is the foundation of the scheme's security; compromise of the private key generally undermines both confidentiality and any assurance of origin.
Encryption and Decryption Roles
In a confidentiality use case, a sender encrypts with the recipient's public key and only the recipient's private key can decrypt. This separation removes the need to pre-share a secret key over the same channel.
Digital Signatures
Asymmetric techniques can also support signing, where a holder signs with a private key and others verify with the corresponding public key, providing assurance of integrity and origin rather than confidentiality.
Key Distribution and Trust
Because public keys are shared openly, binding a public key to a verified identity typically depends on supporting trust mechanisms such as certificates or a public key infrastructure. This entry does not cover the mechanics of any specific certificate or trust framework.

Common questions

Answers to the questions practitioners most commonly ask about Asymmetric Encryption.

Does encrypting personal data with asymmetric encryption make it no longer personal data?
No. Applying asymmetric encryption does not remove data from the scope of data protection regimes such as the EU GDPR or UK GDPR. Encrypted personal data generally remains personal data, because the mapping between ciphertext and the underlying individual can typically be reversed by parties holding the relevant private key. Encryption is best understood as a security control that supports confidentiality, not as a technique that anonymizes data. This is closer in effect to pseudonymization, which is reversible and still treated as personal data, than to irreversible anonymization. This answer does not address when, if ever, data might be considered effectively anonymized in a specific factual context.
Is asymmetric encryption a governance control or a security control?
Asymmetric encryption is primarily an information security control, contributing to the confidentiality and, through related mechanisms such as digital signatures, the integrity of data. It is not in itself a data governance measure, which typically concerns ownership, stewardship, data quality, lineage, cataloging, and policy. The two domains overlap in practice: governance policies may mandate the use of encryption, and demonstrating that such controls are implemented can support accountability. However, deploying encryption alone does not satisfy governance obligations, which generally require demonstrable evidence rather than the presence of a single technical measure.
How does asymmetric encryption differ from symmetric encryption in practical deployments?
Asymmetric encryption uses a mathematically related key pair, a public key and a private key, so that data encrypted with one key is decrypted with the other, while symmetric encryption uses a single shared secret key for both operations. In practice, asymmetric operations are typically more computationally intensive, so many systems use asymmetric encryption to establish trust or to exchange a symmetric session key, and then use symmetric encryption for the bulk of the data. This entry does not cover specific algorithm choices, key lengths, or performance benchmarks, which depend on implementation and current cryptographic guidance.
What key management responsibilities accompany the use of asymmetric encryption?
Because the private key can reverse the protection, its confidentiality is central to the control's effectiveness. Typical responsibilities include secure generation, storage, distribution, rotation, and revocation of keys, along with clear assignment of who holds and who can access each key. Where processing is carried out on behalf of another party, the allocation of key control between a controller and a processor is generally a matter to be defined and documented. This entry does not prescribe a specific key management standard, and it does not address certificate authority or public key infrastructure design in detail.
Can asymmetric encryption help demonstrate accountability under data protection and governance frameworks?
It can contribute to, but does not by itself establish, accountability. Frameworks such as the EU GDPR and UK GDPR, ISO/IEC 27701, and the NIST Privacy Framework generally treat accountability as requiring demonstrable evidence of appropriate measures, and encryption may be cited among technical measures adopted. Evidence typically includes documented policies, records of implementation, and management of the underlying keys. No single control, including asymmetric encryption, guarantees compliance, which depends on context, jurisdiction, and implementation. This entry does not address which specific measures a given assessment might require.
Where does asymmetric encryption fit relative to obligations like transfer safeguards or breach handling?
Asymmetric encryption is one technical measure that may be relevant to several obligations, but this entry does not define those obligations or their scope. Whether encryption affects the treatment of a security incident, or supports a particular cross-border transfer arrangement, depends on the applicable regime and the specific facts, and treatment differs across jurisdictions such as those under the EU GDPR, UK GDPR, CCPA and CPRA, and HIPAA. This entry does not cover cross-border transfer mechanics, retention rules, breach notification thresholds, or enforcement outcomes.

Common misconceptions

Encrypting personal data with asymmetric encryption makes it non-personal, taking it out of scope of data protection law.
Encryption is a security control, not a de-identification technique. Encrypted personal data generally remains personal data because it can be restored to plaintext with the appropriate key. In most jurisdictions it is treated at most as pseudonymized data, which is still personal data, rather than anonymized data. This entry does not address the specific treatment of encrypted data under any particular regime.
Asymmetric encryption is simply a stronger or more advanced replacement for symmetric encryption.
The two serve different purposes and are typically used together. Asymmetric methods address key distribution and signing, while symmetric methods are generally more efficient for encrypting larger volumes of data. Choosing one over the other depends on the use case rather than a general notion of strength.
Deploying asymmetric encryption by itself demonstrates compliance with data protection obligations.
Encryption may support security and accountability requirements, but no single control guarantees compliance. Accountability under governance frameworks generally requires demonstrable evidence across policies, key management, and broader controls, and compliance depends on context, jurisdiction, and implementation. This entry does not cover retention, cross-border transfer, or enforcement matters.

Best practices

Protect private keys as the critical secret in the scheme, restricting access to authorized holders and treating any compromise as a security incident affecting both confidentiality and assurance of origin.
Establish a trust mechanism, such as certificates or a public key infrastructure, to bind public keys to verified identities rather than assuming an openly shared public key is authentic.
Do not treat encrypted personal data as anonymized or out of scope; continue to apply applicable data protection controls, since such data generally remains personal data.
Combine asymmetric and symmetric techniques according to their strengths, typically using asymmetric methods for key exchange or signing and symmetric methods for bulk data.
Distinguish confidentiality use cases from signing use cases so that keys and processes are applied to their intended purpose and not conflated.
Maintain demonstrable evidence of key management and control implementation to support accountability, rather than relying on the presence of encryption alone.