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 *    Semiconductor ASA integrated circuit in a product or a software update for
 *    such product, must reproduce the above copyright notice, this list of
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 *    materials provided with the distribution.
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 * 3. Neither the name of Nordic Semiconductor ASA nor the names of its
 *    contributors may be used to endorse or promote products derived from this
 *    software without specific prior written permission.
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 * 4. This software, with or without modification, must only be used with a
 *    Nordic Semiconductor ASA integrated circuit.
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/**@file
 * Ed25519 is a specific implementation of EdDSA, a digital signature scheme.
 * EdDSA is based on Twisted Edwards curves and is designed to be faster than
 * existing digital signature schemes without sacrificing security. It was
 * developed by Daniel J. Bernstein, et al. Ed25519 is intended to provide
 * attack resistance comparable to quality 128-bit symmetric ciphers.
 * 
 * @see [Ed25519: high-speed high-security signatures](https://ed25519.cr.yp.to)
 */

#ifndef OCC_ED25519_H
#define OCC_ED25519_H

#include <stdint.h>
#include <stddef.h>


/**
 * Length of a public key.
 */
#define occ_ed25519_PUBLIC_KEY_BYTES (32)

/**
 * Length of a secret key.
 */
#define occ_ed25519_SECRET_KEY_BYTES (32)

/**
 * Length of a signature.
 */
#define occ_ed25519_BYTES (64)


/**
 * Ed25519 signature key pair generation.
 *
 * Given a secret key `sk`, the corresponding public key is computed and put
 * into `pk`. The key pair can then be used to sign and verify message signatures.
 *
 * **Example**
 * @include occ_ed25519_public_key.c
 *
 * @param[out] pk Generated public key.
 * @param      sk Secret key. Must be prefilled with random data.
 */
void occ_ed25519_public_key(uint8_t pk[occ_ed25519_PUBLIC_KEY_BYTES],
                            const uint8_t sk[occ_ed25519_SECRET_KEY_BYTES]);

/**
 * Ed25519 signature generate.
 *
 * The message @p m is signed using the secret key @p sk and the corresponding
 * public key @p pk. The signature is put into @p sig.
 *
 * **Example**
 * @include occ_ed25519_sign.c
 *
 * @param[out] sig   Generated signature.
 * @param      m     Input message.
 * @param      m_len Length of @p m.
 * @param      sk    Secret key.
 * @param      pk    Public key.
 */
void occ_ed25519_sign(uint8_t sig[occ_ed25519_BYTES],
                      const uint8_t *m, size_t m_len,
                      const uint8_t sk[occ_ed25519_SECRET_KEY_BYTES],
                      const uint8_t pk[occ_ed25519_PUBLIC_KEY_BYTES]);

/**
 * Ed25519 signature verification.
 * 
 * The signature @p sig of the input message @p m is verified using the signer's
 * public key @p pk.
 *
 * **Example**
 * @include occ_ed25519_verify.c
 * 
 * @param sig   Input signature.
 * @param m     Input message.
 * @param m_len Length of @p m.
 * @param pk    Signer's public key.
 *
 * @returns 0 If signature OK.
 * @returns -1 Otherwise.
 */
int occ_ed25519_verify(const uint8_t sig[occ_ed25519_BYTES],
                       const uint8_t *m, size_t m_len,
                       const uint8_t pk[occ_ed25519_PUBLIC_KEY_BYTES]);

#endif
