FreeBSD/Linux Kernel Cross Reference
sys/crypto/openssl/ossl_chacha.h

     /*
      * Copyright 2015-2018 The OpenSSL Project Authors. All Rights Reserved.
      *
      * Licensed under the OpenSSL license (the "License").  You may not use
      * this file except in compliance with the License.  You can obtain a copy
      * in the file LICENSE in the source distribution or at
      * https://www.openssl.org/source/license.html
      */
     
    /* From include/crypto/chacha.h */
    
    #ifndef OSSL_CRYPTO_CHACHA_H
    #define OSSL_CRYPTO_CHACHA_H
    
    /*
     * ChaCha20_ctr32 encrypts |len| bytes from |inp| with the given key and
     * nonce and writes the result to |out|, which may be equal to |inp|.
     * The |key| is not 32 bytes of verbatim key material though, but the
     * said material collected into 8 32-bit elements array in host byte
     * order. Same approach applies to nonce: the |counter| argument is
     * pointer to concatenated nonce and counter values collected into 4
     * 32-bit elements. This, passing crypto material collected into 32-bit
     * elements as opposite to passing verbatim byte vectors, is chosen for
     * efficiency in multi-call scenarios.
     */
    void ChaCha20_ctr32(unsigned char *out, const unsigned char *inp,
                        size_t len, const unsigned int key[8],
                        const unsigned int counter[4]);
    /*
     * You can notice that there is no key setup procedure. Because it's
     * as trivial as collecting bytes into 32-bit elements, it's reckoned
     * that below macro is sufficient.
     */
    #define CHACHA_U8TOU32(p)  ( \
                    ((unsigned int)(p)[0])     | ((unsigned int)(p)[1]<<8) | \
                    ((unsigned int)(p)[2]<<16) | ((unsigned int)(p)[3]<<24)  )
    
    #define CHACHA_KEY_SIZE         32
    #define CHACHA_CTR_SIZE         16
    #define CHACHA_BLK_SIZE         64
    
    #endif

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