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ChaCha20 DRNG
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ChaCha20 DRNG

The ChaCha20 DRNG is a complete standalone implementation of a deterministic random number generator. It does not need any external cryptographic support.

The ChaCha20 DRNG is implemented using ideas specified in SP800-90A, AIS 20/31 as well as specified by Peter Gutmann's 1998 Usenix Security Symposium paper: "Software Generation of Practically Strong Random Numbers". The following list enumerates the different properties offered with the ChaCha20 DRNG.


The ChaCha20 DRNG user space implementation was developed to allow an in-depth study of the DRNG for its use as part of the Linux Random Number Generator.

Both implementations with respect to the pseudo random number generator are identical. Naturally, the ChaCha20 DRNG user space includes the ChaCha20 block operation, self tests and the pulling of data from seed sources.

Seed Sources

The ChaCha20 DRNG code base allows the following seed sources to be used. These seed sources are enabled or disabled in the Makefile. If more than one seed source is enabled, the seed of all seed sources is concatenated.

  • Jitter RNG: If the file jitterentropy-base.c exists in the current directory, the Jitter RNG is used as noise source.

  • getrandom system call

  • /dev/random device file

Directory Structure

base directory -- directory holding the library

test/ -- functional verification code

The code in each directory is intended to be compiled independently.

Version Numbers

The version numbers for this library have the following schema: MAJOR.MINOR.PATCHLEVEL

Changes in the major number implies API and ABI incompatible changes, or functional changes that require consumer to be updated (as long as this number is zero, the API is not considered stable and can change without a bump of the major version).

Changes in the minor version are API compatible, but the ABI may change. Functional enhancements only are added. Thus, a consumer can be left unchanged if enhancements are not considered. The consumer only needs to be recompiled.

Patchlevel changes are API / ABI compatible. No functional changes, no enhancements are made. This release is a bug fixe release only. The consumer can be left unchanged and does not need to be recompiled.

Make Targets

The following make targets are applicable:

  • make # compile library

  • make install # install library into $PREFIX

  • make scan # use CLANG static code analyzer

  • make man # compile man pages in doc/man

  • make maninstall # install man pages into $PREFIX

  • make pdf # generate documentation in PDF

  • make ps # generate documentation in PS

  • make html # generate documentation as HTML in doc/html


The Makefile compiles ChaCha20 DRNG as a shared library.

The "install" Makefile target installs libkcapi under /usr/local/lib or /usr/local/lib64. The header file is installed to /usr/local/include.

Test cases

The test/ directory contains test cases to verify the correct operation of this library.


Stephan Mueller

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