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118 lines
3.9 KiB
Plaintext
118 lines
3.9 KiB
Plaintext
=pod
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=head1 NAME
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EVP_KEYEXCH-ECDH - ECDH Key Exchange algorithm support
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=head1 DESCRIPTION
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Key exchange support for the B<ECDH> key type.
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=head2 ECDH Key Exchange parameters
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=over 4
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=item "ecdh-cofactor-mode" (B<OSSL_EXCHANGE_PARAM_EC_ECDH_COFACTOR_MODE>) <integer>
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Sets or gets the ECDH mode of operation for the associated key exchange ctx.
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In the context of an Elliptic Curve Diffie-Hellman key exchange, this parameter
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can be used to select between the plain Diffie-Hellman (DH) or Cofactor
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Diffie-Hellman (CDH) variants of the key exchange algorithm.
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When setting, the value should be 1, 0 or -1, respectively forcing cofactor mode
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on, off, or resetting it to the default for the private key associated with the
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given key exchange ctx.
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When getting, the value should be either 1 or 0, respectively signaling if the
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cofactor mode is on or off.
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See also L<provider-keymgmt(7)> for the related
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B<OSSL_PKEY_PARAM_USE_COFACTOR_ECDH> parameter that can be set on a
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per-key basis.
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=item "kdf-type" (B<OSSL_EXCHANGE_PARAM_KDF_TYPE>) <UTF8 string>
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See L<provider-keyexch(7)/Common Key Exchange parameters>.
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=item "kdf-digest" (B<OSSL_EXCHANGE_PARAM_KDF_DIGEST>) <UTF8 string>
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See L<provider-keyexch(7)/Common Key Exchange parameters>.
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=item "kdf-digest-props" (B<OSSL_EXCHANGE_PARAM_KDF_DIGEST_PROPS>) <UTF8 string>
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See L<provider-keyexch(7)/Common Key Exchange parameters>.
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=item "kdf-outlen" (B<OSSL_EXCHANGE_PARAM_KDF_OUTLEN>) <unsigned integer>
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See L<provider-keyexch(7)/Common Key Exchange parameters>.
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=item "kdf-ukm" (B<OSSL_EXCHANGE_PARAM_KDF_UKM>) <octet string>
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See L<provider-keyexch(7)/Common Key Exchange parameters>.
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=back
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=head1 EXAMPLES
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Keys for the host and peer must be generated as shown in
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L<EVP_PKEY-EC(7)/Examples> using the same curve name.
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The code to generate a shared secret for the normal case is identical to
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L<EVP_KEYEXCH-DH(7)/Examples>.
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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 but also using X963KDF with a user key material:
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/* It is assumed that the host_key, peer_pub_key and ukm are set up */
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void derive_secret(EVP_PKEY *host_key, EVP_PKEY *peer_key,
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unsigned char *ukm, size_t ukm_len)
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{
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unsigned char secret[64];
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size_t out_len = sizeof(secret);
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size_t secret_len = out_len;
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unsigned int pad = 1;
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OSSL_PARAM params[6];
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EVP_PKEY_CTX *dctx = EVP_PKEY_CTX_new_from_pkey(NULL, host_key, NULL);
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EVP_PKEY_derive_init(dctx);
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params[0] = OSSL_PARAM_construct_uint(OSSL_EXCHANGE_PARAM_PAD, &pad);
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params[1] = OSSL_PARAM_construct_utf8_string(OSSL_EXCHANGE_PARAM_KDF_TYPE,
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"X963KDF", 0);
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params[2] = OSSL_PARAM_construct_utf8_string(OSSL_EXCHANGE_PARAM_KDF_DIGEST,
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"SHA1", 0);
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params[3] = OSSL_PARAM_construct_size_t(OSSL_EXCHANGE_PARAM_KDF_OUTLEN,
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&out_len);
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params[4] = OSSL_PARAM_construct_octet_string(OSSL_EXCHANGE_PARAM_KDF_UKM,
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ukm, ukm_len);
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params[5] = OSSL_PARAM_construct_end();
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EVP_PKEY_CTX_set_params(dctx, params);
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EVP_PKEY_derive_set_peer(dctx, peer_pub_key);
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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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=head1 SEE ALSO
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L<EVP_PKEY-EC(7)>
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L<EVP_PKEY(3)>,
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L<provider-keyexch(7)>,
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L<provider-keymgmt(7)>,
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L<OSSL_PROVIDER-default(7)>,
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L<OSSL_PROVIDER-FIPS(7)>,
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=head1 COPYRIGHT
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Copyright 2020-2022 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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