mirror of https://github.com/openssl/openssl.git
176 lines
4.5 KiB
Plaintext
176 lines
4.5 KiB
Plaintext
=pod
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=head1 NAME
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EVP_KDF_SSHKDF - The SSHKDF EVP_KDF implementation
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=head1 DESCRIPTION
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Support for computing the B<SSHKDF> KDF through the B<EVP_KDF> API.
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The EVP_KDF_SSHKDF algorithm implements the SSHKDF key derivation function.
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It is defined in RFC 4253, section 7.2 and is used by SSH to derive IVs,
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encryption keys and integrity keys.
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Five inputs are required to perform key derivation: The hashing function
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(for example SHA256), the Initial Key, the Exchange Hash, the Session ID,
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and the derivation key type.
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=head2 Numeric identity
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B<EVP_KDF_SSHKDF> 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_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_SET_SSHKDF_XCGHASH>
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=item B<EVP_KDF_CTRL_SET_SSHKDF_SESSION_ID>
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These controls expect two arguments: C<unsigned char *buffer>, C<size_t length>
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They set the respective values to the first B<length> bytes of the buffer
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B<buffer>. If a value is already set, the contents are replaced.
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EVP_KDF_ctrl_str() takes two type strings for these controls:
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=over 4
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=item "xcghash"
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=item "session_id"
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The value string is used as is.
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=item "hexxcghash"
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=item "hexsession_id"
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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_SSHKDF_TYPE>
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This control expects one argument: C<int mode>
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Sets the type for the SSHHKDF operation. There are six supported types:
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=over 4
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=item EVP_KDF_SSHKDF_TYPE_INITIAL_IV_CLI_TO_SRV
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The Initial IV from client to server.
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A single char of value 65 (ASCII char 'A').
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=item EVP_KDF_SSHKDF_TYPE_INITIAL_IV_SRV_TO_CLI
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The Initial IV from server to client
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A single char of value 66 (ASCII char 'B').
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=item EVP_KDF_SSHKDF_TYPE_ENCRYPTION_KEY_CLI_TO_SRV
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The Encryption Key from client to server
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A single char of value 67 (ASCII char 'C').
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=item EVP_KDF_SSHKDF_TYPE_ENCRYPTION_KEY_SRV_TO_CLI
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The Encryption Key from server to client
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A single char of value 68 (ASCII char 'D').
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=item EVP_KDF_SSHKDF_TYPE_INTEGRITY_KEY_CLI_TO_SRV
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The Integrity Key from client to server
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A single char of value 69 (ASCII char 'E').
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=item EVP_KDF_SSHKDF_TYPE_INTEGRITY_KEY_SRV_TO_CLI
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The Integrity Key from client to server
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A single char of value 70 (ASCII char 'F').
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=back
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EVP_KDF_ctrl_str() type string: "type"
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The value is a string of length one character. The only valid values
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are the numerical values of the ASCII characters: "A" (65) to "F" (70).
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=back
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=head1 NOTES
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A context for SSHKDF can be obtained by calling:
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EVP_KDF_CTX *kctx = EVP_KDF_CTX_new_id(EVP_KDF_SSHKDF);
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The output length of the SSHKDF derivation is specified via the C<keylen>
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parameter to the L<EVP_KDF_derive(3)> function.
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Since the SSHKDF output length is variable, calling L<EVP_KDF_size()>
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to obtain the requisite length is not meaningful. The caller must
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allocate a buffer of the desired length, and pass that buffer to the
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L<EVP_KDF_derive(3)> function along with the desired length.
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=head1 EXAMPLES
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This example derives an 8 byte IV using SHA-256 with a 1K "key" and appropriate
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"xcghash" and "session_id" values:
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EVP_KDF_CTX *kctx;
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unsigned char key[1024] = "01234...";
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unsigned char xcghash[32] = "012345...";
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unsigned char session_id[32] = "012345...";
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unsigned char out[8];
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size_t outlen = sizeof(out);
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kctx = EVP_KDF_CTX_new_id(EVP_KDF_SSHKDF);
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if (EVP_KDF_CTX_set_md(kctx, EVP_sha256()) <= 0)
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/* Error */
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if (EVP_KDF_CTX_set1_key(kctx, key, 1024) <= 0)
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/* Error */
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if (EVP_KDF_CTX_set1_sshkdf_xcghash(kctx, xcghash, 32) <= 0)
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/* Error */
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if (EVP_KDF_CTX_set1_sshkdf_session_id(kctx, session_id, 32) <= 0)
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/* Error */
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if (EVP_KDF_CTX_set_sshkdf_type(kctx,
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EVP_KDF_SSHKDF_TYPE_INITIAL_IV_CLI_TO_SRV) <= 0)
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/* Error */
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if (EVP_KDF_derive(kctx, out, &outlen) <= 0)
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/* Error */
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=head1 CONFORMING TO
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RFC 4253
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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 OpenSSL license (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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