ChaCha20 - Crypto++ Wiki (2024)

ChaCha is a family of stream ciphers by Daniel J. Bernstein based on a variant of Salsa20. Also see ChaCha, a variant of Salsa20.

The 20-round stream cipher ChaCha/20 is consistently faster than AES and is recommended by the designer for typical cryptographic applications. The reduced-round ciphers ChaCha/12 and ChaCha/8 are among the fastest 256-bit stream ciphers available and are recommended for applications where speed is more important than confidence.

Crypto++ provides all stream ciphers from eSTREAM Phase 3 for Profile 1. The ciphers are ChaCha, HC-128/256, Rabbit, Salsa20 and Sosemanuk. The IETF's version of ChaCha is specified in RFC 7539, ChaCha20 and Poly1305 for IETF Protocols and available as ChaChaTLS.

If you are used to working in languages like Java or libraries like OpenSSL, then you might want to visit the Init-Update-Final wiki page. Crypto++ provides the transformation model, but its not obvious because its often shrouded behind Pipelines.

ChaCha20 AVX2 implementation had a bug related to carries. On occasion the tail of the cipher text would be incorrect. The bug appeared to be relatively rare when the cpu had AVX2, and it did not appear in other implementations like SSE or NEON. The bug was fixed in Crypto++ 8.6. Also see Issue 1069 and Commit 20962baf4440.

Note: if your project is using encryption alone to secure your data, encryption alone is usually not enough. Please take a moment to read Authenticated Encryption and consider using an algorithm or mode like CCM, GCM, EAX or ChaCha20Poly1305.

Key and IV sizes

The first sample program prints ChaCha20's key and iv sizes.

int main(){ using namespace CryptoPP; ChaCha::Encryption enc; std::cout << "key length: " << enc.DefaultKeyLength() << std::endl; std::cout << "key length (min): " << enc.MinKeyLength () << std::endl; std::cout << "key length (max): " << enc.MaxKeyLength () << std::endl; std::cout << "iv size: " << enc.IVSize() << std::endl; return 0;}

A typical output is shown below.

<console>$ ./test.exekey length: 32key length (min): 16key length (max): 32iv size: 8</console>

Encryption and Decryption

The following example shows you how to use ChaCha::Encryption and ChaCha::Decryption. &cipher[0] may look odd, but its how to get the non-const pointer from a std::string.

#include "cryptlib.h"#include "secblock.h"#include "chacha.h"#include "osrng.h"#include "files.h"#include "hex.h"#include <iostream>#include <string>int main(){ using namespace CryptoPP; AutoSeededRandomPool prng; std::string plain("My Plaintext!! My Dear plaintext!!"), cipher, recover; SecByteBlock key(32), iv(8); prng.GenerateBlock(key, key.size()); prng.GenerateBlock(iv, iv.size()); std::cout << "Key: "; encoder.Put((const byte*)key.data(), key.size()); encoder.MessageEnd(); std::cout << std::endl; std::cout << "IV: "; encoder.Put((const byte*)iv.data(), iv.size()); encoder.MessageEnd(); std::cout << std::endl; // Encryption object ChaCha::Encryption enc; enc.SetKeyWithIV(key, key.size(), iv, iv.size()); // Perform the encryption cipher.resize(plain.size()); enc.ProcessData((byte*)&cipher[0], (const byte*)plain.data(), plain.size()); std::cout << "Plain: " << plain << std::endl; std::cout << "Cipher: "; encoder.Put((const byte*)cipher.data(), cipher.size()); encoder.MessageEnd(); std::cout << std::endl; ChaCha::Decryption dec; dec.SetKeyWithIV(key, key.size(), iv, iv.size()); // Perform the decryption recover.resize(cipher.size()); dec.ProcessData((byte*)&recover[0], (const byte*)cipher.data(), cipher.size()); std::cout << "Recovered: " << recover << std::endl; return 0;}

A typical output is shown below, including the non-printable characters from encryption.

$ ./test.exeKey: F21CD8583F951808A01C16963AC4AD23FC356625D9BACE17825FDEC3BBA1A932IV: 7BAD60605518A681Plain: My Plaintext!! My Dear plaintext!!Cipher: B942A12358DA90A33581BE13CB17BEFA2C37FBA40FDD3A1D42AC0778B824F25F8F85Recovered: My Plaintext!! My Dear plaintext!!

Resynchronizing

The ChaCha family is self-inverting so you can use the encryption object for decryption (and vice versa). The cipher holds internal state and is resynchronizable. If you want to reuse an encryption or decryption object then you should set the IV with Resynchronize.

#include "cryptlib.h"#include "secblock.h"#include "chacha.h"#include "osrng.h"#include "files.h"#include "hex.h"#include <iostream>#include <string>int main(){ using namespace CryptoPP; AutoSeededRandomPool prng; HexEncoder encoder(new FileSink(std::cout)); std::string plain("My Plaintext!! My Dear plaintext!!"), cipher, recover; SecByteBlock key(32), iv(8); prng.GenerateBlock(key, key.size()); prng.GenerateBlock(iv, iv.size()); std::cout << "Key: "; encoder.Put((const byte*)key.data(), key.size()); encoder.MessageEnd(); std::cout << std::endl; std::cout << "IV: "; encoder.Put((const byte*)iv.data(), iv.size()); encoder.MessageEnd(); std::cout << std::endl; // Encryption object ChaCha::Encryption enc; enc.SetKeyWithIV(key, key.size(), iv, iv.size()); // Perform the encryption cipher.resize(plain.size()); enc.ProcessData((byte*)&cipher[0], (const byte*)plain.data(), plain.size()); std::cout << "Plain: " << plain << std::endl; std::cout << "Cipher: "; encoder.Put((const byte*)cipher.data(), cipher.size()); encoder.MessageEnd(); std::cout << std::endl; // ChaCha::Decryption dec; // dec.SetKeyWithIV(key, key.size(), iv, iv.size()); std::cout << "Self inverting: " << enc.IsSelfInverting() << std::endl; std::cout << "Resynchronizable: " << enc.IsResynchronizable() << std::endl; enc.Resynchronize(iv, iv.size()); // Perform the decryption // recover.resize(cipher.size()); // dec.ProcessData((byte*)&recover[0], (const byte*)cipher.data(), cipher.size()); // Perform the decryption with the encryptor recover.resize(cipher.size()); enc.ProcessData((byte*)&recover[0], (const byte*)cipher.data(), cipher.size()); std::cout << "Recovered: " << recover << std::endl; return 0;}

A typical output is shown below, including the non-printable characters from encryption.

$ ./test.exeKey: A636E0F7E4053DBCDD26F86377EAC4A156D85C0608728BD60EDCFE7DE5969A01IV: AAB018DBCF485646Plain: My Plaintext!! My Dear plaintext!!Cipher: 7327EF99A66F1E4B09910B2DA3F2AB3B508E0EA6AC35DB916D31927DA214A707BEB3Self inverting: 1Resynchronizable: 1Recovered: My Plaintext!! My Dear plaintext!!

The following C++11 program demonstrates resynchronizing without the additional operations like printing a key or iv. The library was built with CXXFLAGS="-DNDEBUG -g2 -O3 -std=c++11.

#include "cryptlib.h"#include "chacha.h"#include <iostream>#include <array>#include <cstdint>int main(int argc, char *argv[]){ using namespace CryptoPP; const uint8_t chachaKey[16] = "012345678901234"; const uint8_t chachaIV[8] = "0123456"; ChaCha::Encryption enc; ChaCha::Decryption dec; enc.SetKeyWithIV(chachaKey, 16, chachaIV, 8); dec.SetKeyWithIV(chachaKey, 16, chachaIV, 8); std::array<byte, 3> origin = { 1,2,3 }; std::array<byte, 3> encrpyt; enc.ProcessData(encrpyt.data(), origin.data(), origin.size()); std::array<byte, 3> decrypt; dec.ProcessData(decrypt.data(), encrpyt.data(), encrpyt.size()); dec.Resynchronize(chachaIV, sizeof(chachaIV)); dec.ProcessData(decrypt.data(), encrpyt.data(), encrpyt.size()); dec.Resynchronize(chachaIV, sizeof(chachaIV)); dec.ProcessData(decrypt.data(), encrpyt.data(), encrpyt.size()); std::cout << (int)decrypt[0] << " " << (int)decrypt[1] << " "; std::cout << (int)decrypt[2] << std::endl; return 0;}

It produces the following result.

$ g++ -DNDEBUG -g2 -O3 -std=c++11 test.cxx -o test.exe ./libcryptopp.a$ ./test.exe1 2 3

Pipelines

You can also use stream ciphers in a Pipeline. Below is an example of ChaCha20 participating in a pipeline. Internally, StreamTransformationFilter calls ProcessData on the incoming data stream. The filter also buffers output if there is no attached transformation or sink.

#include "cryptlib.h"#include "secblock.h"#include "filters.h"#include "chacha.h"#include "osrng.h"#include "files.h"#include "hex.h"#include <iostream>#include <string>int main(){ using namespace CryptoPP; AutoSeededRandomPool prng; HexEncoder encoder(new FileSink(std::cout)); std::string plain("My Plaintext!! My Dear plaintext!!"), cipher, recover; SecByteBlock key(32), iv(8); prng.GenerateBlock(key, key.size()); prng.GenerateBlock(iv, iv.size()); std::cout << "Key: "; encoder.Put(key.data(), key.size()); encoder.MessageEnd(); std::cout << std::endl; std::cout << "IV: "; encoder.Put(iv.data(), iv.size()); encoder.MessageEnd(); std::cout << std::endl; // Encryption object ChaCha::Encryption enc; enc.SetKeyWithIV(key, key.size(), iv, iv.size()); // Decryption object ChaCha::Decryption dec; dec.SetKeyWithIV(key, key.size(), iv, iv.size()); StringSource ss1(plain, true, new StreamTransformationFilter(enc, new StringSink(cipher))); StringSource ss2(cipher, true, new StreamTransformationFilter(dec, new StringSink(recover))); std::cout << "Plain: " << plain << std::endl; std::cout << "Cipher: "; encoder.Put((const byte*)cipher.data(), cipher.size()); encoder.MessageEnd(); std::cout << std::endl; std::cout << "Recovered: " << recover << std::endl; return 0;}

The program produces the expected output:

$ ./test.exeKey: 784175D9D0E9C5DD30EE0D8F4580EED256BF39DF1E425CF8621155D3636C38CEIV: A85CFCD4DFBB47F1Plain: My Plaintext!! My Dear plaintext!!Cipher: FA51C2BD26615D7CE04A97553E35E3A849419D60B7B5711586DC20611B86B08E0082Recovered: My Plaintext!! My Dear plaintext!!

Rounds

The examples above use ChaCha with 20 rounds. 20 rounds is the default configuration and nothing special needs to be done for it. To use a different number of rounds then pass a Rounds parameter using a NameValuePairs when configuring the ChaCha object.

#include "cryptlib.h"#include "secblock.h"#include "algparam.h"#include "argnames.h"#include "filters.h"#include "chacha.h"#include "osrng.h"#include "files.h"#include "hex.h"#include <iostream>#include <string>int main(){ using namespace CryptoPP; AutoSeededRandomPool prng; HexEncoder encoder(new FileSink(std::cout)); std::string plain("My Plaintext!! My Dear plaintext!!"), cipher, recover; SecByteBlock key(32), iv(8); prng.GenerateBlock(key, key.size()); prng.GenerateBlock(iv, iv.size()); std::cout << "Key: "; encoder.Put(key.data(), key.size()); encoder.MessageEnd(); std::cout << std::endl; std::cout << "IV: "; encoder.Put(iv.data(), iv.size()); encoder.MessageEnd(); std::cout << std::endl; // Additional parameters to configure object const AlgorithmParameters params = MakeParameters(Name::Rounds(), 12) (Name::IV(), ConstByteArrayParameter(iv, 8)); // Encryption object ChaCha::Encryption enc; enc.SetKey(key, key.size(), params); // Decryption object ChaCha::Decryption dec; dec.SetKey(key, key.size(), params); StringSource ss1(plain, true, new StreamTransformationFilter(enc, new StringSink(cipher))); StringSource ss2(cipher, true, new StreamTransformationFilter(dec, new StringSink(recover))); std::cout << "Plain: " << plain << std::endl; std::cout << "Cipher: "; encoder.Put((const byte*)cipher.data(), cipher.size()); encoder.MessageEnd(); std::cout << std::endl; std::cout << "Recovered: " << recover << std::endl; return 0;}