Field-level encryption for REST APIs locks down sensitive values at the granularity of individual fields. Instead of encrypting the entire body, you target specific keys—credit card numbers, Social Security numbers, API tokens—and encrypt them before they leave the client. On the server, you decrypt only when absolutely required. This design gives you finer control, limits blast radius after a breach, and reduces compliance burden under regulations like GDPR and HIPAA.
A field-level encryption REST API works by applying asymmetric or symmetric encryption to selected fields in requests and responses. The client can encrypt using the public key, and the server later decrypts using its private key. For write operations, you can encrypt before sending data to your backend. For read operations, the server encrypts sensitive fields before sending them back to the client. Intermediaries—logs, caches, proxies—see only ciphertext.
Implementing this starts with defining an encryption schema. Map out the fields in each endpoint that require protection. Use strong, standardized algorithms like AES-256 or RSA-2048 paired with proper key management via KMS solutions. Version your encryption keys to allow seamless rotation without downtime. Always enforce TLS at the transport level, but remember it doesn't replace field-level encryption—it only protects the channel, not the payload at rest.
On the client side, integrate encryption logic before serialization. Libraries in languages like Node.js, Python, Go, and Java offer straightforward APIs for AES and RSA. On the server side, handle decryption in controlled modules. Avoid storing plaintext in memory longer than necessary. Audit your encryption process with tests that confirm only the intended fields are encrypted and decrypted.