283 lines
10 KiB
Groff
Executable File
283 lines
10 KiB
Groff
Executable File
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.\" ========================================================================
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.\"
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.IX Title "EVP_PKEY_CTX_SET_HKDF_MD 3"
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.TH EVP_PKEY_CTX_SET_HKDF_MD 3 "2020-03-02" "3.0.0-dev" "OpenSSL"
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.\" For nroff, turn off justification. Always turn off hyphenation; it makes
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.\" way too many mistakes in technical documents.
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.if n .ad l
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.nh
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.SH "NAME"
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EVP_PKEY_CTX_set_hkdf_md, EVP_PKEY_CTX_set1_hkdf_salt,
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EVP_PKEY_CTX_set1_hkdf_key, EVP_PKEY_CTX_add1_hkdf_info,
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EVP_PKEY_CTX_hkdf_mode \-
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HMAC\-based Extract\-and\-Expand key derivation algorithm
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.SH "SYNOPSIS"
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.IX Header "SYNOPSIS"
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.Vb 1
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\& #include <openssl/kdf.h>
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\&
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\& int EVP_PKEY_CTX_hkdf_mode(EVP_PKEY_CTX *pctx, int mode);
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\&
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\& int EVP_PKEY_CTX_set_hkdf_md(EVP_PKEY_CTX *pctx, const EVP_MD *md);
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\&
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\& int EVP_PKEY_CTX_set1_hkdf_salt(EVP_PKEY_CTX *pctx, unsigned char *salt,
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\& int saltlen);
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\&
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\& int EVP_PKEY_CTX_set1_hkdf_key(EVP_PKEY_CTX *pctx, unsigned char *key,
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\& int keylen);
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\&
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\& int EVP_PKEY_CTX_add1_hkdf_info(EVP_PKEY_CTX *pctx, unsigned char *info,
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\& int infolen);
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.Ve
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.SH "DESCRIPTION"
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.IX Header "DESCRIPTION"
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The \s-1EVP_PKEY_HKDF\s0 algorithm implements the \s-1HKDF\s0 key derivation function.
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\&\s-1HKDF\s0 follows the \*(L"extract-then-expand\*(R" paradigm, where the \s-1KDF\s0 logically
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consists of two modules. The first stage takes the input keying material
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and \*(L"extracts\*(R" from it a fixed-length pseudorandom key K. The second stage
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\&\*(L"expands\*(R" the key K into several additional pseudorandom keys (the output
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of the \s-1KDF\s0).
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.PP
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\&\fIEVP_PKEY_CTX_hkdf_mode()\fR sets the mode for the \s-1HKDF\s0 operation. There are three
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modes that are currently defined:
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.IP "\s-1EVP_PKEY_HKDEF_MODE_EXTRACT_AND_EXPAND\s0" 4
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.IX Item "EVP_PKEY_HKDEF_MODE_EXTRACT_AND_EXPAND"
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This is the default mode. Calling \fIEVP_PKEY_derive\fR\|(3) on an \s-1EVP_PKEY_CTX\s0 set
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up for \s-1HKDF\s0 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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.Sp
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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 or an error occurs.
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.IP "\s-1EVP_PKEY_HKDEF_MODE_EXTRACT_ONLY\s0" 4
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.IX Item "EVP_PKEY_HKDEF_MODE_EXTRACT_ONLY"
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In this mode calling \fIEVP_PKEY_derive\fR\|(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.
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.Sp
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The digest, key and salt values must be set before a key is derived or an
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error occurs.
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.IP "\s-1EVP_PKEY_HKDEF_MODE_EXPAND_ONLY\s0" 4
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.IX Item "EVP_PKEY_HKDEF_MODE_EXPAND_ONLY"
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In this mode calling \fIEVP_PKEY_derive\fR\|(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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.Sp
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The digest, key and info values must be set before a key is derived or an
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error occurs.
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.PP
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\&\fIEVP_PKEY_CTX_set_hkdf_md()\fR sets the message digest associated with the \s-1HKDF\s0.
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.PP
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\&\fIEVP_PKEY_CTX_set1_hkdf_salt()\fR sets the salt to \fBsaltlen\fR bytes of the
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buffer \fBsalt\fR. Any existing value is replaced.
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.PP
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\&\fIEVP_PKEY_CTX_set1_hkdf_key()\fR sets the key to \fBkeylen\fR bytes of the buffer
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\&\fBkey\fR. Any existing value is replaced.
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.PP
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\&\fIEVP_PKEY_CTX_add1_hkdf_info()\fR sets the info value to \fBinfolen\fR bytes of the
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buffer \fBinfo\fR. If a value is already set, it is appended to the existing
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value.
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.SH "STRING CTRLS"
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.IX Header "STRING CTRLS"
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\&\s-1HKDF\s0 also supports string based control operations via
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\&\fIEVP_PKEY_CTX_ctrl_str\fR\|(3).
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The \fBtype\fR parameter \*(L"md\*(R" uses the supplied \fBvalue\fR as the name of the digest
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algorithm to use.
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The \fBtype\fR parameter \*(L"mode\*(R" uses the values \*(L"\s-1EXTRACT_AND_EXPAND\s0\*(R",
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\&\*(L"\s-1EXTRACT_ONLY\s0\*(R" and \*(L"\s-1EXPAND_ONLY\s0\*(R" to determine the mode to use.
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The \fBtype\fR parameters \*(L"salt\*(R", \*(L"key\*(R" and \*(L"info\*(R" use the supplied \fBvalue\fR
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parameter as a \fBseed\fR, \fBkey\fR or \fBinfo\fR value.
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The names \*(L"hexsalt\*(R", \*(L"hexkey\*(R" and \*(L"hexinfo\*(R" are similar except they take a hex
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string which is converted to binary.
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.SH "NOTES"
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.IX Header "NOTES"
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All these functions are implemented as macros.
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.PP
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A context for \s-1HKDF\s0 can be obtained by calling:
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.PP
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.Vb 1
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\& EVP_PKEY_CTX *pctx = EVP_PKEY_CTX_new_id(EVP_PKEY_HKDF, NULL);
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.Ve
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.PP
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The total length of the info buffer cannot exceed 1024 bytes in length: this
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should be more than enough for any normal use of \s-1HKDF\s0.
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.PP
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The output length of an \s-1HKDF\s0 expand operation is specified via the length
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parameter to the \fIEVP_PKEY_derive\fR\|(3) function.
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Since the \s-1HKDF\s0 output length is variable, passing a \fB\s-1NULL\s0\fR buffer as a means
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to obtain the requisite length is not meaningful with \s-1HKDF\s0 in any mode that
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performs an expand operation. Instead, the caller must allocate a buffer of the
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desired length, and pass that buffer to \fIEVP_PKEY_derive\fR\|(3) along with (a
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pointer initialized to) the desired length. Passing a \fB\s-1NULL\s0\fR buffer to obtain
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the length is allowed when using \s-1EVP_PKEY_HKDEF_MODE_EXTRACT_ONLY\s0.
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.PP
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Optimised versions of \s-1HKDF\s0 can be implemented in an \s-1ENGINE\s0.
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.SH "RETURN VALUES"
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.IX Header "RETURN VALUES"
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All these functions return 1 for success and 0 or a negative value for failure.
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In particular a return value of \-2 indicates the operation is not supported by
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the public key algorithm.
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.SH "EXAMPLES"
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.IX Header "EXAMPLES"
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This example derives 10 bytes using \s-1SHA\-256\s0 with the secret key \*(L"secret\*(R",
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salt value \*(L"salt\*(R" and info value \*(L"label\*(R":
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.PP
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.Vb 4
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\& EVP_PKEY_CTX *pctx;
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\& unsigned char out[10];
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\& size_t outlen = sizeof(out);
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\& pctx = EVP_PKEY_CTX_new_id(EVP_PKEY_HKDF, NULL);
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\&
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\& if (EVP_PKEY_derive_init(pctx) <= 0)
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\& /* Error */
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\& if (EVP_PKEY_CTX_set_hkdf_md(pctx, EVP_sha256()) <= 0)
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\& /* Error */
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\& if (EVP_PKEY_CTX_set1_hkdf_salt(pctx, "salt", 4) <= 0)
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\& /* Error */
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\& if (EVP_PKEY_CTX_set1_hkdf_key(pctx, "secret", 6) <= 0)
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\& /* Error */
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\& if (EVP_PKEY_CTX_add1_hkdf_info(pctx, "label", 5) <= 0)
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\& /* Error */
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\& if (EVP_PKEY_derive(pctx, out, &outlen) <= 0)
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\& /* Error */
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.Ve
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.SH "CONFORMING TO"
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.IX Header "CONFORMING TO"
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\&\s-1RFC\s0 5869
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.SH "SEE ALSO"
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.IX Header "SEE ALSO"
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\&\fIEVP_PKEY_CTX_new\fR\|(3),
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\&\fIEVP_PKEY_CTX_ctrl_str\fR\|(3),
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\&\fIEVP_PKEY_derive\fR\|(3)
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.SH "COPYRIGHT"
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.IX Header "COPYRIGHT"
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Copyright 2016\-2018 The OpenSSL Project Authors. All Rights Reserved.
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.PP
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Licensed under the Apache License 2.0 (the \*(L"License\*(R"). 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 \s-1LICENSE\s0 in the source distribution or at
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<https://www.openssl.org/source/license.html>.
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