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Hi,</div>
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after studying the different key generator functions more closely I came to the conclusion that, since the Prime256 curve has a cofactor of 1, both KDF should produce the same value and so everything has cleared up.</div>
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Kind regards,</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
Henning</div>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> openssl-users <openssl-users-bounces@openssl.org> on behalf of Henning Krause via openssl-users <openssl-users@openssl.org><br>
<b>Sent:</b> Sunday, May 23, 2021 2:45 PM<br>
<b>To:</b> openssl-users@openssl.org <openssl-users@openssl.org><br>
<b>Subject:</b> Support for ECDH One-pass in "openssl cms enc"</font>
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Hi,</div>
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I'm trying to encrypt an email using the ECDH One-Pass algorithm. I've first created an X509 certificate with an EDSA key based on the curve prime256v1.</div>
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Then, I ran this command:</div>
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openssl cms -encrypt -in Unencrypted.eml -binary -recip ecc.cer -aes256 -keyopt ecdh_kdf_md:sha256 -keyopt ecdh_cofactor_mode:1<br>
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This does indeed create an encrypted eml:</div>
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MIME-Version: 1.0
<div>Content-Disposition: attachment; filename="smime.p7m"</div>
<div>Content-Type: application/pkcs7-mime; smime-type=enveloped-data; name="smime.p7m"</div>
<div>Content-Transfer-Encoding: base64</div>
<div><br>
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<div>MIIBuQYJKoZIhvcNAQcDoIIBqjCCAaYCAQIxggEQoYIBDAIBA6BRoU8wCQYHKoZI</div>
<div>zj0CAQNCAAQYMD63JbNHczeD0BVjdlzuZAdTyFchu/KsXAZA6/OmbJ37xEoga1GG</div>
<div>ItMUW5qnzzNL9L25wi1GVZrMxH5bksxEMBUGBiuBBAEOATALBglghkgBZQMEAS0w</div>
<div>gZwwgZkwbTBnMQswCQYDVQQGEwJERTEMMAoGA1UECAwDTlJXMRIwEAYDVQQHDAlQ</div>
<div>YWRlcmJvcm4xGTAXBgNVBAoMEE5ldCBhdCBXb3JrIEdtYkgxGzAZBgNVBAMMEk5v</div>
<div>U3BhbVByb3h5IERldiBDQQICEBwEKB6t+YrcLQLXlVc8oC47Ija4mgzJ0uv7DvFl</div>
<div>JQXtUGZpf4pYQ9fvEO0wgYwGCSqGSIb3DQEHATAdBglghkgBZQMEASoEENsnhiim</div>
<div>ZK1xDpAN3tpDiwmAYLp71os2uX6TIEJeDbtAuEf570gNii9AdHgdbS3+4hpFUyKI</div>
<div>fifnofwQRq5+vsIc8DllYGMdMoWknO0vzNSNaLFpWMJ2Xe0SFyU0dO30wHlHXvz3</div>
a3CzwXa5yoQ1qHfo3Q==<br>
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And it does have the expected KEK encryption algorithm set:</div>
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1.3.132.1.14.1 => dhSinglePass-cofactorDH-sha256kdf-scheme<br>
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However, the KDF method used is exactly the same as when I execute:</div>
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<span style="background-color:rgb(255,255,255); display:inline!important">openssl cms -encrypt -in Unencrypted.eml -binary -recip ecc.cer -aes256 -keyopt ecdh_kdf_md:sha256 -keyopt ecdh_cofactor_mode:0</span><br>
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This call does produce a different KEK algorithm:</div>
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1.3.132.1.11.1 ecdhX963KDF-SHA256.<br>
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<span style="background-color:rgb(255,255,255); display:inline!important"><br>
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<span style="background-color:rgb(255,255,255); display:inline!important">At least I can decrypt the content encryption key in both cases using the same algorithm ('Standard' ECDH).</span></div>
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<span style="background-color:rgb(255,255,255); display:inline!important"><br>
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<span style="background-color:rgb(255,255,255); display:inline!important">I'm using OpenSSL 3.0.0-beta1-dev (Library: OpenSSL 3.0.0-beta1-dev ).</span></div>
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<span style="background-color:rgb(255,255,255); display:inline!important"><br>
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<span style="background-color:rgb(255,255,255); display:inline!important">Any ideas? Do I need any additional parameters to get this working?</span></div>
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<span style="background-color:rgb(255,255,255); display:inline!important">Kind regards,</span></div>
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<span style="background-color:rgb(255,255,255); display:inline!important">Henning</span></div>
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