[null,null,["最后更新时间 (UTC)：2025-07-25。"],[[["\u003cp\u003eHybrid Encryption combines symmetric and asymmetric encryption for efficient and secure data exchange, allowing anyone to encrypt with a public key but only the private key holder to decrypt.\u003c/p\u003e\n"],["\u003cp\u003eIt ensures confidentiality through randomization and requires the same context information used during encryption for successful decryption.\u003c/p\u003e\n"],["\u003cp\u003eTink recommends the \u003ccode\u003eDHKEM_X25519_HKDF_SHA256_HKDF_SHA256_AES_256_GCM\u003c/code\u003e key type, implementing the HPKE standard for robust security.\u003c/p\u003e\n"],["\u003cp\u003eWhile providing privacy, Hybrid Encryption does not inherently guarantee authenticity, requiring separate sender authentication mechanisms if needed.\u003c/p\u003e\n"]]],["Hybrid Encryption combines public key cryptography's convenience with symmetric encryption's efficiency. Senders generate a symmetric key to encrypt each message's plaintext and encapsulate it with the recipient's public key. Recipients decapsulate the key and decrypt the ciphertext. It ensures secrecy, asymmetry, and randomization. It includes `context_info`, public data that binds to the ciphertext for integrity checks. `DHKEM_X25519_HKDF_SHA256_HKDF_SHA256_AES_256_GCM` is recommended, implementing HPKE for key encapsulation, derivation, and authenticated encryption. It only provides privacy, not authenticity.\n"],null,["# Hybrid Encryption\n\nThe Hybrid Encryption primitive combines the efficiency of symmetric encryption\nwith the convenience of public key (asymmetric) cryptography. Anyone can encrypt\ndata using the public key, but only users with the private key can decrypt the\ndata.\n\nFor Hybrid Encryption, the sender generates a fresh symmetric key to encrypt the\nplaintext of each message to produce a ciphertext. That symmetric key is\n*encapsulated* with the recipient's public key. For Hybrid Decryption, the\nsymmetric key is *decapsulated* by the recipient and then used to decrypt the\nciphertext to recover the original plaintext. See [Tink Hybrid Encryption wire\nformat](/tink/wire-format#hybrid_encryption) for details on how to store or\ntransmit the ciphertext along with the key encapsulation.\n\nHybrid Encryption has the following properties:\n\n- **Secrecy**: No one is able to get any information about the encrypted plaintext (except the length), unless they have access to the private key.\n- **Asymmetry**: Encrypting the ciphertext can be done with the public key, but for decryption, the private key is required.\n- **Randomization**: The encryption is randomized. Two messages with the same plaintext will not yield the same ciphertext. This prevents attackers from knowing which ciphertext corresponds to a given plaintext.\n\nHybrid Encryption is represented in Tink as a pair of primitives:\n\n- *HybridEncrypt* for encryption\n- *HybridDecrypt* for decryption\n\n### Context info parameter\n\nIn addition to the plaintext, Hybrid Encryption accepts an extra parameter,\n`context_info`, which is usually public data implicit from the context, but\nshould be bound to the resulting ciphertext. This means that the ciphertext\nallows you to confirm the integrity of the context info but there are no\nguarantees for its secrecy or authenticity. The actual context info can be empty\nor null, but to ensure the correct decryption of the resulting ciphertext, the\nsame context info value must be provided for decryption.\n\nA concrete implementation of Hybrid Encryption can bind context info to the\nciphertext in various ways, for example:\n\n- Use `context_info` as associated data input for AEAD symmetric encryption (cf. [RFC 5116](https://tools.ietf.org/html/rfc5116)).\n- Use `context_info` as \"CtxInfo\" input for HKDF (if the implementation uses HKDF as key derivation function, cf. [RFC\n 5869](https://tools.ietf.org/html/rfc5869)).\n\n### Choose a key type\n\nWe recommend using the **`DHKEM_X25519_HKDF_SHA256_HKDF_SHA256_AES_256_GCM`**\nkey type for most use cases. This key type implements the Hybrid Public Key\nEncryption (HPKE) standard as specified in [RFC\n9180](https://www.rfc-editor.org/rfc/rfc9180.html). HPKE consists\nof a key encapsulation mechanism (KEM), a key derivation function (KDF), and an\nauthenticated encryption with associated data (AEAD) algorithm.\n\n`DHKEM_X25519_HKDF_SHA256_HKDF_SHA256_AES_256_GCM` specifically employs:\n\n- KEM: Diffie--Hellman over Curve25519 with HKDF-SHA-256 to derive the shared secret.\n- KDF: HKDF-SHA-256 to derive the sender and receiver context.\n- AEAD: AES-256-GCM with 12-byte nonces generated according to the HPKE standard.\n\nOther supported HPKE key types include, but are not limited to, the following:\n\n- `DHKEM_X25519_HKDF_SHA256_HKDF_SHA256_AES_128_GCM`\n- `DHKEM_X25519_HKDF_SHA256_HKDF_SHA256_CHACHA20_POLY1305`\n- `DHKEM_P256_HKDF_SHA256_HKDF_SHA256_AES_128_GCM`\n- `DHKEM_P521_HKDF_SHA512_HKDF_SHA512_AES_256_GCM`\n\nSee [RFC 9180](https://www.rfc-editor.org/rfc/rfc9180.html) for\nmore details on the algorithm choices for the KEM, KDF, and AEAD.\n\nAlthough no longer recommended, Tink also supports some variations of ECIES as\ndescribed in [Victor Shoup's ISO 18033-2\nstandard](https://www.shoup.net/iso/). Some supported ECIES key\ntypes are listed below:\n\n- `ECIES_P256_HKDF_HMAC_SHA256_AES128_GCM`\n- `ECIES_P256_COMPRESSED_HKDF_HMAC_SHA256_AES128_GCM`\n- `ECIES_P256_HKDF_HMAC_SHA256_AES128_CTR_HMAC_SHA256`\n- `ECIES_P256_COMPRESSED_HKDF_HMAC_SHA256_AES128_CTR_HMAC_SHA256`\n\n### Minimal properties\n\n| **Caution:** Hybrid Encryption only provides privacy, not authenticity. It is only secure if the recipient can accept anonymous messages or rely on other mechanisms to authenticate the sender.\n\n- Plaintext and context info can have arbitrary length (within the range 0..2^32^ bytes)\n- Secure against adaptive chosen ciphertext attacks\n- 128-bit security for elliptic curve based schemes\n\n### Example use cases\n\nSee I want to [exchange data](/tink/exchange-data)."]]
