5a285addbf
Changed PKEY/KDF API to call the new API. Added wrappers for PKCS5_PBKDF2_HMAC() and EVP_PBE_scrypt() to call the new EVP KDF APIs. Documentation updated. Reviewed-by: Paul Dale <paul.dale@oracle.com> Reviewed-by: Richard Levitte <levitte@openssl.org> (Merged from https://github.com/openssl/openssl/pull/6674)
180 lines
5.1 KiB
Text
180 lines
5.1 KiB
Text
=pod
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=head1 NAME
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EVP_KDF_HKDF - The HKDF EVP_KDF implementation
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=head1 DESCRIPTION
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Support for computing the B<HKDF> KDF through the B<EVP_KDF> API.
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The EVP_KDF_HKDF algorithm implements the HKDF key derivation function.
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HKDF follows the "extract-then-expand" paradigm, where the KDF logically
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consists of two modules. The first stage takes the input keying material
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and "extracts" from it a fixed-length pseudorandom key K. The second stage
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"expands" the key K into several additional pseudorandom keys (the output
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of the KDF).
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=head2 Numeric identity
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B<EVP_KDF_HKDF> is the numeric identity for this implementation; it
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can be used with the EVP_KDF_CTX_new_id() function.
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=head2 Supported controls
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The supported controls are:
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=over 4
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=item B<EVP_KDF_CTRL_SET_SALT>
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=item B<EVP_KDF_CTRL_SET_MD>
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=item B<EVP_KDF_CTRL_SET_KEY>
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These controls work as described in L<EVP_KDF_CTX(3)/CONTROLS>.
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=item B<EVP_KDF_CTRL_RESET_HKDF_INFO>
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This control does not expect any arguments.
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Resets the context info buffer to zero length.
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=item B<EVP_KDF_CTRL_ADD_HKDF_INFO>
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This control expects two arguments: C<unsigned char *info>, C<size_t infolen>
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Sets the info value to the first B<infolen> bytes of the buffer B<info>. If a
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value is already set, the contents of the buffer are appended to the existing
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value.
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The total length of the context info buffer cannot exceed 1024 bytes;
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this should be more than enough for any normal use of HKDF.
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EVP_KDF_ctrl_str() takes two type strings for this control:
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=over 4
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=item "info"
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The value string is used as is.
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=item "hexinfo"
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The value string is expected to be a hexadecimal number, which will be
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decoded before being passed on as the control value.
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=back
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=item B<EVP_KDF_CTRL_SET_HKDF_MODE>
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This control expects one argument: C<int mode>
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Sets the mode for the HKDF operation. There are three modes that are currently
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defined:
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=over 4
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=item EVP_KDF_HKDF_MODE_EXTRACT_AND_EXPAND
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This is the default mode. Calling L<EVP_KDF_derive(3)> on an EVP_KDF_CTX set
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up for HKDF will perform an extract followed by an expand operation in one go.
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The derived key returned will be the result after the expand operation. The
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intermediate fixed-length pseudorandom key K is not returned.
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In this mode the digest, key, salt and info values must be set before a key is
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derived otherwise an error will occur.
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=item EVP_KDF_HKDF_MODE_EXTRACT_ONLY
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In this mode calling L<EVP_KDF_derive(3)> will just perform the extract
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operation. The value returned will be the intermediate fixed-length pseudorandom
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key K. The C<keylen> parameter must match the size of K, which can be looked
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up by calling EVP_KDF_size() after setting the mode and digest.
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The digest, key and salt values must be set before a key is derived otherwise
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an error will occur.
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=item EVP_KDF_HKDF_MODE_EXPAND_ONLY
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In this mode calling L<EVP_KDF_derive(3)> will just perform the expand
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operation. The input key should be set to the intermediate fixed-length
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pseudorandom key K returned from a previous extract operation.
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The digest, key and info values must be set before a key is derived otherwise
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an error will occur.
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=back
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EVP_KDF_ctrl_str() type string: "mode"
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The value string is expected to be one of: "EXTRACT_AND_EXPAND", "EXTRACT_ONLY"
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or "EXPAND_ONLY".
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=back
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=head1 NOTES
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A context for HKDF can be obtained by calling:
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EVP_KDF_CTX *kctx = EVP_KDF_CTX_new_id(EVP_KDF_HKDF);
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The output length of an HKDF expand operation is specified via the C<keylen>
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parameter to the L<EVP_KDF_derive(3)> function. When using
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EVP_KDF_HKDF_MODE_EXTRACT_ONLY the C<keylen> parameter must equal the size of
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the intermediate fixed-length pseudorandom key otherwise an error will occur.
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For that mode, the fixed output size can be looked up by calling EVP_KDF_size()
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after setting the mode and digest on the C<EVP_KDF_CTX>.
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=head1 EXAMPLE
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This example derives 10 bytes using SHA-256 with the secret key "secret",
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salt value "salt" and info value "label":
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EVP_KDF_CTX *kctx;
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unsigned char out[10];
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kctx = EVP_KDF_CTX_new_id(EVP_KDF_HKDF);
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if (EVP_KDF_ctrl(kctx, EVP_KDF_CTRL_SET_MD, EVP_sha256()) <= 0) {
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error("EVP_KDF_CTRL_SET_MD");
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}
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if (EVP_KDF_ctrl(kctx, EVP_KDF_CTRL_SET_SALT, "salt", (size_t)4) <= 0) {
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error("EVP_KDF_CTRL_SET_SALT");
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}
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if (EVP_KDF_ctrl(kctx, EVP_KDF_CTRL_SET_KEY, "secret", (size_t)6) <= 0) {
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error("EVP_KDF_CTRL_SET_KEY");
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}
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if (EVP_KDF_ctrl(kctx, EVP_KDF_CTRL_ADD_HKDF_INFO, "label", (size_t)5) <= 0) {
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error("EVP_KDF_CTRL_ADD_HKDF_INFO");
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}
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if (EVP_KDF_derive(kctx, out, sizeof(out)) <= 0) {
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error("EVP_KDF_derive");
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}
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EVP_KDF_CTX_free(kctx);
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=head1 CONFORMING TO
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RFC 5869
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=head1 SEE ALSO
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L<EVP_KDF_CTX>,
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L<EVP_KDF_CTX_new_id(3)>,
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L<EVP_KDF_CTX_free(3)>,
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L<EVP_KDF_ctrl(3)>,
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L<EVP_KDF_size(3)>,
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L<EVP_KDF_derive(3)>,
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L<EVP_KDF_CTX(3)/CONTROLS>
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=head1 COPYRIGHT
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Copyright 2016-2018 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the Apache License 2.0 (the "License"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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