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/**@file
 * @defgroup nrf_oberon_ed25519 Ed25519 APIs
 * @ingroup nrf_oberon
 * @{
 * @brief Type declarations and APIs for the Ed25519 algorithm.
 *
 * 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 OCRYPTO_ED25519_H
#define OCRYPTO_ED25519_H

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

#ifdef __cplusplus
extern "C" {
#endif

/**
 * Length of a public key.
 */
#define ocrypto_ed25519_PUBLIC_KEY_BYTES (32)

/**
 * Length of a secret key.
 */
#define ocrypto_ed25519_SECRET_KEY_BYTES (32)

/**
 * Length of a signature.
 */
#define ocrypto_ed25519_BYTES (64)


/**
 * Ed25519 signature key pair generation.
 *
 * Given a secret key @p sk, the corresponding public key is computed and put
 * into @p pk. The key pair can then be used to sign and verify message signatures.
 *
 * @param[out] pk Generated public key.
 * @param      sk Secret key. Must be pre-filled with random data.
 */
void ocrypto_ed25519_public_key(uint8_t pk[ocrypto_ed25519_PUBLIC_KEY_BYTES],
                                const uint8_t sk[ocrypto_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.
 *
 * @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 ocrypto_ed25519_sign(uint8_t sig[ocrypto_ed25519_BYTES],
                          const uint8_t *m, size_t m_len,
                          const uint8_t sk[ocrypto_ed25519_SECRET_KEY_BYTES],
                          const uint8_t pk[ocrypto_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.
 *
 * @param sig   Input signature.
 * @param m     Input message.
 * @param m_len Length of @p m.
 * @param pk    Signer's public key.
 *
 * @retval 0  If the signature is valid.
 * @retval -1 Otherwise.
 */
int ocrypto_ed25519_verify(const uint8_t sig[ocrypto_ed25519_BYTES],
                           const uint8_t *m, size_t m_len,
                           const uint8_t pk[ocrypto_ed25519_PUBLIC_KEY_BYTES]);

#ifdef __cplusplus
}
#endif

#endif /* #ifndef OCRYPTO_ED25519_H */

/** @} */