Update KDF documentation (section 7)

Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/9662)

1 files changed, 111 insertions, 0 deletions

diff --git a/doc/man7/EVP_KDF-X963.pod b/doc/man7/EVP_KDF-X963.pod
new file mode 100644
index 0000000000..537d8c5fc5
--- /dev/null
+++ b/doc/man7/EVP_KDF-X963.pod
@@ -0,0 +1,111 @@
+=pod
+
+=head1 NAME
+
+EVP_KDF-X963 - The X9.63-2001 EVP_KDF implementation
+
+=head1 DESCRIPTION
+
+The EVP_KDF-X963 algorithm implements the key derivation function (X963KDF).
+X963KDF is used by Cryptographic Message Syntax (CMS) for EC KeyAgreement, to
+derive a key using input such as a shared secret key and shared info.
+
+=head2 Identity
+
+"X963KDF" is the name for this implementation; it
+can be used with the EVP_KDF_fetch() function.
+
+=head2 Supported parameters
+
+The supported parameters are:
+
+=over 4
+
+=item B<OSSL_KDF_PARAM_PROPERTIES> ("properties") <UTF8 string>
+
+=item B<OSSL_KDF_PARAM_DIGEST> ("digest") <UTF8 string>
+
+These parameters work as described in L<EVP_KDF(3)/PARAMETERS>.
+
+=item B<OSSL_KDF_PARAM_KEY> ("key") <octet string>
+
+The shared secret used for key derivation.
+This parameter sets the secret.
+
+=item B<OSSL_KDF_PARAM_INFO> ("info") <octet string>
+
+This parameter specifies an optional value for shared info.
+
+=back
+
+=head1 NOTES
+
+X963KDF is very similar to the SSKDF that uses a digest as the auxiliary function,
+X963KDF appends the counter to the secret, whereas SSKDF prepends the counter.
+
+A context for X963KDF can be obtained by calling:
+
+ EVP_KDF *kdf = EVP_KDF_fetch(NULL, "X963KDF", NULL);
+ EVP_KDF_CTX *kctx = EVP_KDF_CTX_new(kdf);
+
+The output length of an X963KDF is specified via the C<keylen>
+parameter to the L<EVP_KDF-derive(3)> function.
+
+=head1 EXAMPLES
+
+This example derives 10 bytes, with the secret key "secret" and sharedinfo
+value "label":
+
+ EVP_KDF *kdf;
+ EVP_KDF_CTX *kctx;
+ unsigned char out[10];
+ OSSL_PARAM params[4], *p = params;
+
+ kdf = EVP_KDF_fetch(NULL, "X963KDF", NULL);
+ kctx = EVP_KDF_CTX_new(kdf);
+ EVP_KDF_free(kdf);
+
+ *p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_DIGEST,
+                                         SN_sha256, strlen(SN_sha256));
+ *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SECRET,
+                                          "secret", (size_t)6);
+ *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_INFO,
+                                          "label", (size_t)5);
+ *p = OSSL_PARAM_construct_end();
+ if (EVP_KDF_set_params(kctx, params) <= 0) {
+     error("EVP_KDF_set_params");
+ }
+ if (EVP_KDF_derive(kctx, out, sizeof(out)) <= 0) {
+     error("EVP_KDF_derive");
+ }
+
+ EVP_KDF_CTX_free(kctx);
+
+=head1 CONFORMING TO
+
+"SEC 1: Elliptic Curve Cryptography"
+
+=head1 SEE ALSO
+
+L<EVP_KDF>,
+L<EVP_KDF-CTX_new_id(3)>,
+L<EVP_KDF-CTX_free(3)>,
+L<EVP_KDF-ctrl(3)>,
+L<EVP_KDF-size(3)>,
+L<EVP_KDF-derive(3)>,
+L<EVP_KDF-CTX(3)/PARAMETERS>
+
+=head1 HISTORY
+
+This functionality was added to OpenSSL 3.0.
+
+=head1 COPYRIGHT
+
+Copyright 2019 The OpenSSL Project Authors. All Rights Reserved.
+
+Licensed under the Apache License 2.0 (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