What is the difference between symmetric and asymmetric encryption?

Symmetric methods use one shared key for encryption and decryption; they are fast but require the key to be exchanged securely. Asymmetric methods work with a key pair of public and private key and solve the exchange problem, but are considerably slower. In practice the two are combined.

Which method and key length are appropriate?

That cannot be answered in the abstract, because recommendations shift with computing power and the state of cryptanalysis. The reference is the BSI's Technical Guideline TR-02102, which assesses methods and parameters on an ongoing basis. What matters is reviewing the methods in use against the current edition on a fixed cycle.

Does full-disk encryption replace an entitlement concept?

No. It protects data on a device that is switched off or has gone missing. Once the system is running and a user is signed in, access control alone decides who sees which data. The two measures address different risks and are not interchangeable.

What does end-to-end encryption mean?

The data is encrypted at the sender and decrypted only at the recipient; the systems and providers in between cannot read the content. That offers the strongest protection against access by the provider, but shifts the entire responsibility for the keys to the endpoints — including the question of how a lost key is handled.

How should keys be stored?

Separately from the encrypted data, with access for as few named people as possible, in storage intended for the purpose such as a key vault or a hardware security module. Every key needs an owner, a rule for rotation and a documented recovery procedure that is itself protected.

Encryption: Methods, Use and Key Management

Encryption is the technical measure most often named and least often implemented in full. The reason is rarely the technology: the methods and libraries are available and well tested. The effort lies in the questions of who holds which keys, where they are kept, how they are rotated, and what happens when one is lost.

Symmetric and asymmetric

Feature	Symmetric	Asymmetric
Key	one shared key for encryption and decryption	a key pair of public and private key
Speed	high, suitable for large volumes of data	considerably slower
Core problem	exchanging the shared key securely	binding the public key to an identity
Typical use	storage media, databases, archives, backups	key exchange, signatures, certificates

The two are combined in real systems: an asymmetric method negotiates a symmetric session key, which then encrypts the actual data. That is exactly how the common transport protocols work.

Where encryption is applied

In transit: connections between user and application, between systems, and across leased lines. The most common failing is not the missing encryption facing outwards but the unencrypted leg inside the internal network.
At rest: storage media, databases, backups, archives. Full-disk encryption protects against theft and disposal, not against a signed-in user with rights that reach too far.
In transfer: file exchange, email attachments, media shipped physically. Here encryption usually fails on how practical it is for the recipient.
End to end: only the two endpoints can read; the systems and providers in between cannot. This is the strongest variant and at the same time the one that places the highest demands on key management.

Key management

Key management is the real core, and it spans the full life cycle: generation with sufficient randomness, distribution, secure storage separate from the encrypted data, access restricted to a few named people, governed rotation, revocation on suspicion of compromise, and controlled destruction at the end. Every key should have a named owner.

Two points come up repeatedly in examinations: keys or passphrases stored in the same systems whose data they protect, and the absence of a recovery procedure. Losing a key means losing the data. Encryption is therefore also an availability risk and belongs in the continuity planning.

Choosing methods

Developing your own cryptographic methods is not appropriate in any use case. What governs is established, publicly reviewed methods in current implementations. For the specific choice of methods and parameters, the BSI publishes Technical Guideline TR-02102, a recommendation kept continuously up to date that can be used as a reference. Because recommendations change over time, reviewing the methods in use belongs on a fixed cycle.

Legal context

Art. 32 GDPR names encryption expressly as one possible measure without prescribing it; what governs remains appropriateness in relation to the risk. Data that is effectively encrypted can limit the consequences of a data breach; whether that removes the need to inform data subjects has to be judged case by case, and with regard to where the keys ended up.

What encryption does not do

It does not protect against authorised but inappropriate access, against malware on an unlocked system, against misconfigured entitlements, or against loss of the data. It replaces neither access control nor backup; it supplements both.

Browse all entries Back to top

Encryption