Latest update

2019-02-22 12:53:31 +09:00
parent 6523a76e2e
commit 25fbda8e8b
186 changed files with 9758 additions and 1640 deletions
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+=pod
+
+=head1 NAME
+
+EVP_KDF_HKDF - The HKDF EVP_KDF implementation
+
+=head1 DESCRIPTION
+
+Support for computing the B<HKDF> KDF through the B<EVP_KDF> API.
+
+The EVP_KDF_HKDF algorithm implements the HKDF key derivation function.
+HKDF follows the "extract-then-expand" paradigm, where the KDF logically
+consists of two modules. The first stage takes the input keying material
+and "extracts" from it a fixed-length pseudorandom key K. The second stage
+"expands" the key K into several additional pseudorandom keys (the output
+of the KDF).
+
+=head2 Numeric identity
+
+B<EVP_KDF_HKDF> is the numeric identity for this implementation; it
+can be used with the EVP_KDF_CTX_new_id() function.
+
+=head2 Supported controls
+
+The supported controls are:
+
+=over 4
+
+=item B<EVP_KDF_CTRL_SET_SALT>
+
+=item B<EVP_KDF_CTRL_SET_MD>
+
+=item B<EVP_KDF_CTRL_SET_KEY>
+
+These controls work as described in L<EVP_KDF_CTX(3)/CONTROLS>.
+
+=item B<EVP_KDF_CTRL_RESET_HKDF_INFO>
+
+This control does not expect any arguments.
+
+Resets the context info buffer to zero length.
+
+=item B<EVP_KDF_CTRL_ADD_HKDF_INFO>
+
+This control expects two arguments: C<unsigned char *info>, C<size_t infolen>
+
+Sets the info value to the first B<infolen> bytes of the buffer B<info>.  If a
+value is already set, the contents of the buffer are appended to the existing
+value.
+
+The total length of the context info buffer cannot exceed 1024 bytes;
+this should be more than enough for any normal use of HKDF.
+
+EVP_KDF_ctrl_str() takes two type strings for this control:
+
+=over 4
+
+=item "info"
+
+The value string is used as is.
+
+=item "hexinfo"
+
+The value string is expected to be a hexadecimal number, which will be
+decoded before being passed on as the control value.
+
+=back
+
+=item B<EVP_KDF_CTRL_SET_HKDF_MODE>
+
+This control expects one argument: C<int mode>
+
+Sets the mode for the HKDF operation. There are three modes that are currently
+defined:
+
+=over 4
+
+=item EVP_KDF_HKDF_MODE_EXTRACT_AND_EXPAND
+
+This is the default mode.  Calling L<EVP_KDF_derive(3)> on an EVP_KDF_CTX set
+up for HKDF will perform an extract followed by an expand operation in one go.
+The derived key returned will be the result after the expand operation. The
+intermediate fixed-length pseudorandom key K is not returned.
+
+In this mode the digest, key, salt and info values must be set before a key is
+derived otherwise an error will occur.
+
+=item EVP_KDF_HKDF_MODE_EXTRACT_ONLY
+
+In this mode calling L<EVP_KDF_derive(3)> will just perform the extract
+operation. The value returned will be the intermediate fixed-length pseudorandom
+key K.  The C<keylen> parameter must match the size of K, which can be looked
+up by calling EVP_KDF_size() after setting the mode and digest.
+
+The digest, key and salt values must be set before a key is derived otherwise
+an error will occur.
+
+=item EVP_KDF_HKDF_MODE_EXPAND_ONLY
+
+In this mode calling L<EVP_KDF_derive(3)> will just perform the expand
+operation. The input key should be set to the intermediate fixed-length
+pseudorandom key K returned from a previous extract operation.
+
+The digest, key and info values must be set before a key is derived otherwise
+an error will occur.
+
+=back
+
+EVP_KDF_ctrl_str() type string: "mode"
+
+The value string is expected to be one of: "EXTRACT_AND_EXPAND", "EXTRACT_ONLY"
+or "EXPAND_ONLY".
+
+=back
+
+=head1 NOTES
+
+A context for HKDF can be obtained by calling:
+
+ EVP_KDF_CTX *kctx = EVP_KDF_CTX_new_id(EVP_KDF_HKDF);
+
+The output length of an HKDF expand operation is specified via the C<keylen>
+parameter to the L<EVP_KDF_derive(3)> function.  When using
+EVP_KDF_HKDF_MODE_EXTRACT_ONLY the C<keylen> parameter must equal the size of
+the intermediate fixed-length pseudorandom key otherwise an error will occur.
+For that mode, the fixed output size can be looked up by calling EVP_KDF_size()
+after setting the mode and digest on the C<EVP_KDF_CTX>.
+
+=head1 EXAMPLE
+
+This example derives 10 bytes using SHA-256 with the secret key "secret",
+salt value "salt" and info value "label":
+
+ EVP_KDF_CTX *kctx;
+ unsigned char out[10];
+
+ kctx = EVP_KDF_CTX_new_id(EVP_KDF_HKDF);
+
+ if (EVP_KDF_ctrl(kctx, EVP_KDF_CTRL_SET_MD, EVP_sha256()) <= 0) {
+     error("EVP_KDF_CTRL_SET_MD");
+ }
+ if (EVP_KDF_ctrl(kctx, EVP_KDF_CTRL_SET_SALT, "salt", (size_t)4) <= 0) {
+     error("EVP_KDF_CTRL_SET_SALT");
+ }
+ if (EVP_KDF_ctrl(kctx, EVP_KDF_CTRL_SET_KEY, "secret", (size_t)6) <= 0) {
+     error("EVP_KDF_CTRL_SET_KEY");
+ }
+ if (EVP_KDF_ctrl(kctx, EVP_KDF_CTRL_ADD_HKDF_INFO, "label", (size_t)5) <= 0) {
+     error("EVP_KDF_CTRL_ADD_HKDF_INFO");
+ }
+ if (EVP_KDF_derive(kctx, out, sizeof(out)) <= 0) {
+     error("EVP_KDF_derive");
+ }
+
+ EVP_KDF_CTX_free(kctx);
+
+=head1 CONFORMING TO
+
+RFC 5869
+
+=head1 SEE ALSO
+
+L<EVP_KDF_CTX>,
+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)/CONTROLS>
+
+=head1 COPYRIGHT
+
+Copyright 2016-2018 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