###### Books / Practical Cryptography for Developers (Unfinished) / Chapter 6b

# ECIES Hybrid Encryption Scheme

A hybrid encryption scheme similar to the previously demonstrated code is standardized under the name **Elliptic Curve Integrated Encryption Scheme** (**ECIES**) in many crypto standards like SECG SEC-1, ISO/IEC 18033-2, IEEE 1363a and ANSI X9.63. **ECIES** is a public-key authenticated encryption scheme, which works similarly to the above code examples, but uses a **KDF** (key-derivation function) for deriving separate **MAC key** and symmetric **encryption key** from the ECDH shared secret. It has many variants.

The **ECIES standard** combines ECC-based **asymmetric cryptography** with **symmetric ciphers** to provide data encryption by EC private key and decryption by the corresponding EC public key. The **ECIES** encryption scheme uses **ECC** cryptography (public key cryptosystem) + key-derivation function (**KDF**) + **symmetric encryption** algorithm + **MAC** algorithm, combined together like it is shown on the figure below:

The input of the **ECIES encryption** consists of recipient’s **public key** + **plain text message**. The output consists of sender’s ephemeral public key (**ciphertext public key**) + **encrypted message** (ciphertext + symmetric algorithm parameters) + **authentication tag** (MAC code):

`ECIES-encrypt(recipientPublicKey, plaintextMessage)`

➔`{ cipherTextPublicKey, encryptedMessage, authTag }`

The **ECIES decryption** takes the output from the encryption + the **recipient’s private key** and produces the original plaintext message or detects a problem (e.g. integrity / authentication error):

`ECIES-decrypt(cipherTextPublicKey, encryptedMessage, authTag, recipientPrivateKey, )`

➔`plaintextMessage`

The ECIES encryption scheme is a **framework**, not a concrete algorithm. It can be implemented by plugging different algorithms, e.g. the **secp256k1** or **P-521** elliptic curve for the public-key calculations + **PBKDF2** or **Scrypt** for KDF function + **AES-CTR** or **AES-GCM** or **ChaCha20-Poly1305** for symmetric cipher and authentication tag + **HMAC-SHA512** for MAC algorithm (in case of unauthenticated encryption).

In the next section we shall demonstrate through a **code example** how to use ECIES in practice.