# Exercises: ECIES Encrypt / Decrypt Write a program to **encrypt** / **decrypt** a **message** by public / private key using [**ECIES**](https://en.wikipedia.org/wiki/Integrated_Encryption_Scheme) (Elliptic Curve Integrated Encryption Scheme). The **encryption** will require an EC **public key** and **decryption** will require the corresponding EC **private key**. Internally, use ECC cryptography based on a **256-bit elliptic curve** by choice (e.g. `brainpoolP256t1`) and **symmetric encryption** by choice (e.g. AES-256-CTR + MAC, AES-128-GCM or ChaCha20-Poly1305), along with **key-derivation function** by choice (e.g. PBKDF2). You are free to choose between writing your **own ECIES implementation**, following the [SECG-SEC-1](http://www.secg.org/sec1-v2.pdf) standard or use a **standard ECIES library** for your language, e.g. * Python: [https://pypi.org/project/eciespy](https://pypi.org/project/eciespy/) * JavaScript: * C#: * Java: * C, C++, PHP, Perl: ## ECIES Encryption Write a program to **encrypt a message** using the **ECIES** hybrid encryption scheme and a **256-bit ECC public key** (2 \* 256 bits). * The **input** consists of the **public key in hex** (at the first line, uncompressed, 128 hex digits) + **plaintext message** for encryption (at the second line). * The **output** is the **hex-encoded encrypted message**. It may hold the ECC ciphertext public key + the ciphertext + MAC code + the symmetric key algorithm parameters, but this depends very much on the underlying algorithms and implementation. **Sample input:** ``` 552e2b308514b38e4989d71ed263e0af6376f65ba81a94ebb74f6fadc223ee80aa8fb710cfb445e0871cd1c1a0c1f2adb2b6eedc2a0470b04244548c5be518c8 Sample text for ECIES encryption. ``` **Sample output:** It will be different for each program execution due to the randomness in the encryption scheme: ``` 0442e2fba3fddba1ba9207f3276e141809782dc72529523aa1fcf35b15c4c22a9333ddacd7d64de4abd0a36138d430c50be7a98d5512cb8c2fe36ca45a0bbd7927c150ae3637c45093207531ce75e3841d4808ced85e82305d8da891708c20479388f6d4a7cde213bb36bf860c5df0077358a942eeb9a4c23e89bcc11f11 ``` ## ECIES Decryption Write a program to **decrypt an encrypted message** created by the program from the previous example, using the **ECIES** hybrid encryption scheme and a **256-bit ECC private key**. * The **input** consists of the **private key in hex** (at the first line, 64 hex digits) + **encrypted message** for decryption (at the second line). * The **output** is the **decrypted plaintext message**. In case or **decryption problem** (e.g. incorrect decryption key or broken encrypted message), display `Error: cannot decrypt the message`. **Sample input:** ``` 27f07d3251dee39ec2c5ff800641f4d839e6f8065033e9a710ea2e519473bdd7 0442e2fba3fddba1ba9207f3276e141809782dc72529523aa1fcf35b15c4c22a9333ddacd7d64de4abd0a36138d430c50be7a98d5512cb8c2fe36ca45a0bbd7927c150ae3637c45093207531ce75e3841d4808ced85e82305d8da891708c20479388f6d4a7cde213bb36bf860c5df0077358a942eeb9a4c23e89bcc11f11 ``` **Sample output:** ``` Sample text for ECIES encryption. ``` **Sample input:** This example holds an incorrect decryption private key: ``` 9ab686c269b2c58f0fca699dde09cf24e23353e56bd60095d681b23709cb0dc3 0442e2fba3fddba1ba9207f3276e141809782dc72529523aa1fcf35b15c4c22a9333ddacd7d64de4abd0a36138d430c50be7a98d5512cb8c2fe36ca45a0bbd7927c150ae3637c45093207531ce75e3841d4808ced85e82305d8da891708c20479388f6d4a7cde213bb36bf860c5df0077358a942eeb9a4c23e89bcc11f11 ``` **Sample output:** ``` Error: cannot decrypt the message ``` --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://cryptobook.nakov.com/asymmetric-key-ciphers/exercises-ecies-encrypt-decrypt.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.