266 lines
9.6 KiB
Plaintext
266 lines
9.6 KiB
Plaintext
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.\" ========================================================================
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.\"
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.IX Title "EVP_KEYEXCH-DH 7ossl"
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.TH EVP_KEYEXCH-DH 7ossl "2024-01-30" "3.2.1" "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_KEYEXCH\-DH
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\&\- DH Key Exchange algorithm support
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.SH "DESCRIPTION"
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.IX Header "DESCRIPTION"
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Key exchange support for the \fB\s-1DH\s0\fR key type.
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.SS "\s-1DH\s0 key exchange parameters"
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.IX Subsection "DH key exchange parameters"
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.ie n .IP """pad"" (\fB\s-1OSSL_EXCHANGE_PARAM_PAD\s0\fR) <unsigned integer>" 4
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.el .IP "``pad'' (\fB\s-1OSSL_EXCHANGE_PARAM_PAD\s0\fR) <unsigned integer>" 4
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.IX Item "pad (OSSL_EXCHANGE_PARAM_PAD) <unsigned integer>"
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Sets the padding mode for the associated key exchange ctx.
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Setting a value of 1 will turn padding on.
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Setting a value of 0 will turn padding off.
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If padding is off then the derived shared secret may be smaller than the
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largest possible secret size.
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If padding is on then the derived shared secret will have its first bytes
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filled with zeros where necessary to make the shared secret the same size as
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the largest possible secret size.
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The padding mode parameter is ignored (and padding implicitly enabled) when
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the \s-1KDF\s0 type is set to \*(L"X942KDF\-ASN1\*(R" (\fB\s-1OSSL_KDF_NAME_X942KDF_ASN1\s0\fR).
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.ie n .IP """kdf-type"" (\fB\s-1OSSL_EXCHANGE_PARAM_KDF_TYPE\s0\fR) <\s-1UTF8\s0 string>" 4
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.el .IP "``kdf-type'' (\fB\s-1OSSL_EXCHANGE_PARAM_KDF_TYPE\s0\fR) <\s-1UTF8\s0 string>" 4
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.IX Item "kdf-type (OSSL_EXCHANGE_PARAM_KDF_TYPE) <UTF8 string>"
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See \*(L"Common Key Exchange parameters\*(R" in \fIprovider\-keyexch\fR\|(7).
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.ie n .IP """kdf-digest"" (\fB\s-1OSSL_EXCHANGE_PARAM_KDF_DIGEST\s0\fR) <\s-1UTF8\s0 string>" 4
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.el .IP "``kdf-digest'' (\fB\s-1OSSL_EXCHANGE_PARAM_KDF_DIGEST\s0\fR) <\s-1UTF8\s0 string>" 4
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.IX Item "kdf-digest (OSSL_EXCHANGE_PARAM_KDF_DIGEST) <UTF8 string>"
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See \*(L"Common Key Exchange parameters\*(R" in \fIprovider\-keyexch\fR\|(7).
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.ie n .IP """kdf-digest-props"" (\fB\s-1OSSL_EXCHANGE_PARAM_KDF_DIGEST_PROPS\s0\fR) <\s-1UTF8\s0 string>" 4
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.el .IP "``kdf-digest-props'' (\fB\s-1OSSL_EXCHANGE_PARAM_KDF_DIGEST_PROPS\s0\fR) <\s-1UTF8\s0 string>" 4
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.IX Item "kdf-digest-props (OSSL_EXCHANGE_PARAM_KDF_DIGEST_PROPS) <UTF8 string>"
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See \*(L"Common Key Exchange parameters\*(R" in \fIprovider\-keyexch\fR\|(7).
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.ie n .IP """kdf-outlen"" (\fB\s-1OSSL_EXCHANGE_PARAM_KDF_OUTLEN\s0\fR) <unsigned integer>" 4
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.el .IP "``kdf-outlen'' (\fB\s-1OSSL_EXCHANGE_PARAM_KDF_OUTLEN\s0\fR) <unsigned integer>" 4
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.IX Item "kdf-outlen (OSSL_EXCHANGE_PARAM_KDF_OUTLEN) <unsigned integer>"
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See \*(L"Common Key Exchange parameters\*(R" in \fIprovider\-keyexch\fR\|(7).
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.ie n .IP """kdf-ukm"" (\fB\s-1OSSL_EXCHANGE_PARAM_KDF_UKM\s0\fR) <octet string>" 4
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.el .IP "``kdf-ukm'' (\fB\s-1OSSL_EXCHANGE_PARAM_KDF_UKM\s0\fR) <octet string>" 4
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.IX Item "kdf-ukm (OSSL_EXCHANGE_PARAM_KDF_UKM) <octet string>"
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See \*(L"Common Key Exchange parameters\*(R" in \fIprovider\-keyexch\fR\|(7).
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.ie n .IP """cekalg"" (\fB\s-1OSSL_KDF_PARAM_CEK_ALG\s0\fR) <octet string ptr>" 4
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.el .IP "``cekalg'' (\fB\s-1OSSL_KDF_PARAM_CEK_ALG\s0\fR) <octet string ptr>" 4
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.IX Item "cekalg (OSSL_KDF_PARAM_CEK_ALG) <octet string ptr>"
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See \*(L"\s-1KDF\s0 Parameters\*(R" in \fIprovider\-kdf\fR\|(7).
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.SH "EXAMPLES"
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.IX Header "EXAMPLES"
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The examples assume a host and peer both generate keys using the same
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named group (or domain parameters). See \*(L"Examples\*(R" in \s-1\fIEVP_PKEY\-DH\s0\fR\|(7).
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Both the host and peer transfer their public key to each other.
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.PP
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To convert the peer's generated key pair to a public key in \s-1DER\s0 format in order
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to transfer to the host:
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.PP
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.Vb 3
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\& EVP_PKEY *peer_key; /* It is assumed this contains the peers generated key */
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\& unsigned char *peer_pub_der = NULL;
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\& int peer_pub_der_len;
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\&
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\& peer_pub_der_len = i2d_PUBKEY(peer_key, &peer_pub_der);
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\& ...
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\& OPENSSL_free(peer_pub_der);
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.Ve
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.PP
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To convert the received peer's public key from \s-1DER\s0 format on the host:
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.PP
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.Vb 4
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\& const unsigned char *pd = peer_pub_der;
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\& EVP_PKEY *peer_pub_key = d2i_PUBKEY(NULL, &pd, peer_pub_der_len);
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\& ...
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\& EVP_PKEY_free(peer_pub_key);
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.Ve
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.PP
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To derive a shared secret on the host using the host's key and the peer's public
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key:
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.PP
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.Vb 8
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\& /* It is assumed that the host_key and peer_pub_key are set up */
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\& void derive_secret(EVP_KEY *host_key, EVP_PKEY *peer_pub_key)
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\& {
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\& unsigned int pad = 1;
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\& OSSL_PARAM params[2];
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\& unsigned char *secret = NULL;
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\& size_t secret_len = 0;
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\& EVP_PKEY_CTX *dctx = EVP_PKEY_CTX_new_from_pkey(NULL, host_key, NULL);
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\&
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\& EVP_PKEY_derive_init(dctx);
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\&
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\& /* Optionally set the padding */
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\& params[0] = OSSL_PARAM_construct_uint(OSSL_EXCHANGE_PARAM_PAD, &pad);
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\& params[1] = OSSL_PARAM_construct_end();
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\& EVP_PKEY_CTX_set_params(dctx, params);
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\&
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\& EVP_PKEY_derive_set_peer(dctx, peer_pub_key);
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\&
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\& /* Get the size by passing NULL as the buffer */
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\& EVP_PKEY_derive(dctx, NULL, &secret_len);
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\& secret = OPENSSL_zalloc(secret_len);
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\&
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\& EVP_PKEY_derive(dctx, secret, &secret_len);
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\& ...
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\& OPENSSL_clear_free(secret, secret_len);
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\& EVP_PKEY_CTX_free(dctx);
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\& }
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.Ve
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.PP
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Very similar code can be used by the peer to derive the same shared secret
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using the host's public key and the peer's generated key pair.
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.SH "SEE ALSO"
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.IX Header "SEE ALSO"
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\&\s-1\fIEVP_PKEY\-DH\s0\fR\|(7),
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\&\s-1\fIEVP_PKEY\-FFC\s0\fR\|(7),
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\&\s-1\fIEVP_PKEY\s0\fR\|(3),
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\&\fIprovider\-keyexch\fR\|(7),
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\&\fIprovider\-keymgmt\fR\|(7),
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\&\fIOSSL_PROVIDER\-default\fR\|(7),
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\&\s-1\fIOSSL_PROVIDER\-FIPS\s0\fR\|(7),
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.SH "COPYRIGHT"
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.IX Header "COPYRIGHT"
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Copyright 2020\-2022 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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