mirror of https://github.com/openssl/openssl.git
164 lines
4.6 KiB
Plaintext
164 lines
4.6 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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The output is considered to be keying material.
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=head2 Identity
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"SSHKDF" is the name for this implementation; it
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can be used with the EVP_KDF_fetch() function.
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=head2 Supported parameters
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The supported parameters are:
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=over 4
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=item "properties" (B<OSSL_KDF_PARAM_PROPERTIES>) <UTF8 string>
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=item "digest" (B<OSSL_KDF_PARAM_DIGEST>) <UTF8 string>
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=item "key" (B<OSSL_KDF_PARAM_KEY>) <octet string>
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These parameters work as described in L<EVP_KDF(3)/PARAMETERS>.
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=item "xcghash" (B<OSSL_KDF_PARAM_SSHKDF_XCGHASH>) <octet string>
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=item "session_id" (B<OSSL_KDF_PARAM_SSHKDF_SESSION_ID>) <octet string>
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These parameters set the respective values for the KDF.
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If a value is already set, the contents are replaced.
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=item "type" (B<OSSL_KDF_PARAM_SSHKDF_TYPE>) <UTF8 string>
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This parameter sets the type for the SSHKDF operation.
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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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=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 *kdf = EVP_KDF_fetch(NULL, "SSHKDF", NULL);
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EVP_KDF_CTX *kctx = EVP_KDF_CTX_new(kdf);
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The output length of the SSHKDF derivation is specified via the I<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_CTX_get_kdf_size(3)>
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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 *kdf;
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EVP_KDF_CTX *kctx;
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char type = EVP_KDF_SSHKDF_TYPE_INITIAL_IV_CLI_TO_SRV;
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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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OSSL_PARAM params[6], *p = params;
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kdf = EVP_KDF_fetch(NULL, "SSHKDF", NULL);
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kctx = EVP_KDF_CTX_new(kdf);
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EVP_KDF_free(kdf);
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*p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_DIGEST,
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SN_sha256, strlen(SN_sha256));
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*p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_KEY,
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key, (size_t)1024);
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*p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SSHKDF_XCGHASH,
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xcghash, (size_t)32);
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*p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SSHKDF_SESSION_ID,
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session_id, (size_t)32);
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*p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_SSHKDF_TYPE,
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&type, sizeof(type));
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*p = OSSL_PARAM_construct_end();
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if (EVP_KDF_derive(kctx, out, outlen, params) <= 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(3)>,
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L<EVP_KDF_CTX_new(3)>,
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L<EVP_KDF_CTX_free(3)>,
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L<EVP_KDF_CTX_set_params(3)>,
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L<EVP_KDF_CTX_get_kdf_size(3)>,
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L<EVP_KDF_derive(3)>,
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L<EVP_KDF(3)/PARAMETERS>
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=head1 HISTORY
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This functionality was added in OpenSSL 3.0.
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=head1 COPYRIGHT
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Copyright 2016-2022 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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