Add Ed25519 documentation

Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/3503)

doc/man3/EVP_DigestSignInit.pod

@@ -59,9 +59,10 @@ The B<EVP> interface to digital signatures should almost always be used in
 preference to the low level interfaces. This is because the code then becomes
 transparent to the algorithm used and much more flexible.
 
-EVP_DigestSign() is a single part operation which signs a single block of data
-in one function. It is equivalent to calling EVP_DigestSignUpdate() and
-EVP_DigestSignFinal().
+EVP_DigestSign() is a one shot operation which signs a single block of data
+in one function. For algorithms that support streaming it is equivalent to
+calling EVP_DigestSignUpdate() and EVP_DigestSignFinal(). For algorithms which
+do not support streaming (e.g. PureEdDSA) it is the only way to sign data.
 
 In previous versions of OpenSSL there was a link between message digest types
 and public key algorithms. This meant that "clone" digests such as EVP_dss1()

doc/man3/EVP_DigestVerifyInit.pod

@@ -57,9 +57,11 @@ The B<EVP> interface to digital signatures should almost always be used in
 preference to the low level interfaces. This is because the code then becomes
 transparent to the algorithm used and much more flexible.
 
-EVP_DigesVerify() is a single part operation which verifies a single block of
-data in one function. It is equivalent to calling EVP_DigestVerifyUpdate() and
-EVP_DigestVerifyFinal().
+EVP_DigesVerify() is a one shot operation which verifies a single block of
+data in one function. For algorithms that support streaming it is equivalent
+to calling EVP_DigestVerifyUpdate() and EVP_DigestVerifyFinal(). For
+algorithms which do not support streaming (e.g. PureEdDSA) it is the only way
+to verify data.
 
 In previous versions of OpenSSL there was a link between message digest types
 and public key algorithms. This meant that "clone" digests such as EVP_dss1()

doc/man7/Ed25519.pod

@@ -0,0 +1,67 @@
+=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