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.\" ========================================================================
.\"
.IX Title "EVP_KEM-EC 7ossl"
.TH EVP_KEM-EC 7ossl "2024-01-30" "3.2.1" "OpenSSL"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
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.nh
.SH "NAME"
EVP_KEM\-EC
\&\- EVP_KEM EC keytype and algorithm support
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
The \fB\s-1EC\s0\fR keytype and its parameters are described in \s-1\fIEVP_PKEY\-EC\s0\fR\|(7).
See \fIEVP_PKEY_encapsulate\fR\|(3) and \fIEVP_PKEY_decapsulate\fR\|(3) for more info.
.SS "\s-1EC KEM\s0 parameters"
.IX Subsection "EC KEM parameters"
.ie n .IP """operation"" (\fB\s-1OSSL_KEM_PARAM_OPERATION\s0\fR)<\s-1UTF8\s0 string>" 4
.el .IP "``operation'' (\fB\s-1OSSL_KEM_PARAM_OPERATION\s0\fR)<\s-1UTF8\s0 string>" 4
.IX Item "operation (OSSL_KEM_PARAM_OPERATION)<UTF8 string>"
The OpenSSL \s-1EC\s0 Key Encapsulation Mechanisms only supports the
following operation:
.RS 4
.ie n .IP """\s-1DHKEM"" \s0(\fB\s-1OSSL_KEM_PARAM_OPERATION_DHKEM\s0\fR)" 4
.el .IP "``\s-1DHKEM'' \s0(\fB\s-1OSSL_KEM_PARAM_OPERATION_DHKEM\s0\fR)" 4
.IX Item "DHKEM (OSSL_KEM_PARAM_OPERATION_DHKEM)"
The encapsulate function generates an ephemeral keypair. It produces keymaterial
by doing an \s-1ECDH\s0 key exchange using the ephemeral private key and a supplied
recipient public key. A \s-1HKDF\s0 operation using the keymaterial and a kem context
then produces a shared secret. The shared secret and the ephemeral public key
are returned.
The decapsulate function uses the recipient private key and the
ephemeral public key to produce the same keymaterial, which can then be used to
produce the same shared secret.
See <https://www.rfc\-editor.org/rfc/rfc9180.html#name\-dh\-based\-kem\-dhkem>
.RE
.RS 4
.Sp
This can be set using either \fIEVP_PKEY_CTX_set_kem_op()\fR or
\&\fIEVP_PKEY_CTX_set_params()\fR.
.RE
.ie n .IP """ikme"" (\fB\s-1OSSL_KEM_PARAM_IKME\s0\fR) <octet string>" 4
.el .IP "``ikme'' (\fB\s-1OSSL_KEM_PARAM_IKME\s0\fR) <octet string>" 4
.IX Item "ikme (OSSL_KEM_PARAM_IKME) <octet string>"
Used to specify the key material used for generation of the ephemeral key.
This value should not be reused for other purposes.
It can only be used for the curves \*(L"P\-256\*(R", \*(L"P\-384\*(R" and \*(L"P\-521\*(R" and should
have a length of at least the size of the encoded private key
(i.e. 32, 48 and 66 for the listed curves).
If this value is not set, then a random ikm is used.
.SH "CONFORMING TO"
.IX Header "CONFORMING TO"
.IP "\s-1RFC9180\s0" 4
.IX Item "RFC9180"
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fIEVP_PKEY_CTX_set_kem_op\fR\|(3),
\&\fIEVP_PKEY_encapsulate\fR\|(3),
\&\fIEVP_PKEY_decapsulate\fR\|(3)
\&\s-1\fIEVP_KEYMGMT\s0\fR\|(3),
\&\s-1\fIEVP_PKEY\s0\fR\|(3),
\&\fIprovider\-keymgmt\fR\|(7)
.SH "HISTORY"
.IX Header "HISTORY"
This functionality was added in OpenSSL 3.2.
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright 2022 The OpenSSL Project Authors. All Rights Reserved.
.PP
Licensed under the Apache License 2.0 (the \*(L"License\*(R").  You may not use
this file except in compliance with the License.  You can obtain a copy
in the file \s-1LICENSE\s0 in the source distribution or at
<https://www.openssl.org/source/license.html>.