| 1 | =pod
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| 2 |
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| 3 | =head1 NAME
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| 4 |
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| 5 | EVP_KEM-X25519, EVP_KEM-X448
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| 6 | - EVP_KEM X25519 and EVP_KEM X448 keytype and algorithm support
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| 7 |
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| 8 | =head1 DESCRIPTION
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| 9 |
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| 10 | The B<X25519> and <X448> keytype and its parameters are described in
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| 11 | L<EVP_PKEY-X25519(7)>.
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| 12 | See L<EVP_PKEY_encapsulate(3)> and L<EVP_PKEY_decapsulate(3)> for more info.
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| 13 |
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| 14 | =head2 X25519 and X448 KEM parameters
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| 15 |
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| 16 | =over 4
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| 17 |
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| 18 | =item "operation" (B<OSSL_KEM_PARAM_OPERATION>)<UTF8 string>
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| 19 |
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| 20 | The OpenSSL X25519 and X448 Key Encapsulation Mechanisms only support the
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| 21 | following operation:
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| 22 |
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| 23 | =over 4
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| 24 |
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| 25 | =item "DHKEM" (B<OSSL_KEM_PARAM_OPERATION_DHKEM>)
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| 26 |
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| 27 | The encapsulate function generates an ephemeral keypair. It produces keymaterial
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| 28 | by doing an X25519 or X448 key exchange using the ephemeral private key and a
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| 29 | supplied recipient public key. A HKDF operation using the keymaterial and a kem
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| 30 | context then produces a shared secret. The shared secret and the ephemeral
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| 31 | public key are returned.
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| 32 | The decapsulate function uses the recipient private key and the
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| 33 | ephemeral public key to produce the same keymaterial, which can then be used to
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| 34 | produce the same shared secret.
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| 35 | See L<https://www.rfc-editor.org/rfc/rfc9180.html#name-dh-based-kem-dhkem>
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| 36 |
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| 37 | =back
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| 38 |
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| 39 | This can be set using either EVP_PKEY_CTX_set_kem_op() or
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| 40 | EVP_PKEY_CTX_set_params().
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| 41 |
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| 42 | =item "ikme" (B<OSSL_KEM_PARAM_IKME>) <octet string>
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| 43 |
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| 44 | Used to specify the key material used for generation of the ephemeral key.
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| 45 | This value should not be reused for other purposes.
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| 46 | It should have a length of at least 32 for X25519, and 56 for X448.
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| 47 | If this value is not set, then a random ikm is used.
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| 48 |
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| 49 | =back
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| 50 |
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| 51 | =head1 CONFORMING TO
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| 52 |
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| 53 | =over 4
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| 54 |
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| 55 | =item RFC9180
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| 56 |
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| 57 | =back
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| 58 |
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| 59 | =head1 SEE ALSO
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| 60 |
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| 61 | L<EVP_PKEY_CTX_set_kem_op(3)>,
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| 62 | L<EVP_PKEY_encapsulate(3)>,
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| 63 | L<EVP_PKEY_decapsulate(3)>
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| 64 | L<EVP_KEYMGMT(3)>,
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| 65 | L<EVP_PKEY(3)>,
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| 66 | L<provider-keymgmt(7)>
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| 67 |
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| 68 | =head1 HISTORY
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| 69 |
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| 70 | This functionality was added in OpenSSL 3.2.
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| 71 |
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| 72 | =head1 COPYRIGHT
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| 73 |
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| 74 | Copyright 2022 The OpenSSL Project Authors. All Rights Reserved.
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| 75 |
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| 76 | Licensed under the Apache License 2.0 (the "License"). You may not use
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| 77 | this file except in compliance with the License. You can obtain a copy
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| 78 | in the file LICENSE in the source distribution or at
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| 79 | L<https://www.openssl.org/source/license.html>.
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| 80 |
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| 81 | =cut
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