=pod

=head1 NAME

Ed25519 - EVP_PKEY Ed25519 support

=head1 DESCRIPTION

The B<Ed25519> EVP_PKEY implementation supports key generation, one shot
digest sign and digest verify using PureEdDSA and B<Ed25519> (see RFC8032).
It has associated private and public key formats compatible with
draft-ietf-curdle-pkix-04.

No additional parameters can be set during key generation one shot signing or
verification. In particular, because PureEdDSA is used, when signing or
verifying a digest must B<NOT> be specified.

=head1 NOTES

The PureEdDSA algorithm does not support the the streaming mechanism
of other signature algorithms using, for example, EVP_DigestUpdate().
The message to sign or verify must be passed using the one shot
EVP_DigestSign() asn EVP_DigestVerify() functions.

When calling EVP_DigestSignInit() or EVP_DigestSignUpdate() the
digest parameter B<MUST> be set to B<NULL>.

Applications wishing to sign certificates (or other structures such as
CRLs or certificate requests) using Ed25519 can either use X509_sign()
or X509_sign_ctx() in the usual way.

A context for the B<Ed25519> algorithm can be obtained by calling:

 EVP_PKEY_CTX *pctx = EVP_PKEY_CTX_new_id(NID_ED25519, NULL);

=head1 EXAMPLE

This example generates an B<ED25519> private key and writes it to standard
output in PEM format:

 #include <openssl/evp.h>
 #include <openssl/pem.h>
 ...
 EVP_PKEY *pkey = NULL;
 EVP_PKEY_CTX *pctx = EVP_PKEY_CTX_new_id(NID_ED25519, NULL);
 EVP_PKEY_keygen_init(pctx);
 EVP_PKEY_keygen(pctx, &pkey);
 EVP_PKEY_CTX_free(pctx);
 PEM_write_PrivateKey(stdout, pkey, NULL, NULL, 0, NULL, NULL);

=head1 SEE ALSO

L<EVP_PKEY_CTX_new(3)>,
L<EVP_PKEY_keygen(3)>,
L<EVP_DigestSignInit(3)>,
L<EVP_DigestVerifyInit(3)>,

=head1 COPYRIGHT

Copyright 2017 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
L<https://www.openssl.org/source/license.html>.

=cut
