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<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">Thanks for the explanation, that probably makes sense.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">Thank you<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;mso-fareast-language:EN-US">Matt<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt"><b><span style="font-size:12.0pt;color:black">From:
</span></b><span style="font-size:12.0pt;color:black">Kyle Hamilton <aerowolf@gmail.com><br>
<b>Date: </b>Monday, 21 November 2022 12:46<br>
<b>To: </b>ORNEST Matej - Contractor <matej.ornest@external.thalesgroup.com><br>
<b>Cc: </b>openssl-users <openssl-users@openssl.org><br>
<b>Subject: </b>Re: X52219/X448 export public key coordinates<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt">The reason has to do with the type of curve representation. X25519 is typically represented in (I believe, but I'm not an expert and I haven't looked at the primary sources recently so take this with a grain
of salt) Montgomery form. Its digital signature counterpart Ed25519 uses the same curve represented in Edwards form.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt">Conversely, the NIST curves are in Weierstrass form. The EC_KEY interface deals solely with Weierstrass form.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt">To my understanding, you can convert any curve to any representation. However, different forms can be acted on with different values at different levels of efficiency, which is why the different forms exist.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt">I hope this helps!<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt">-Kyle H<o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt">On Fri, Nov 18, 2022, 11:47 ORNEST Matej - Contractor via openssl-users <<a href="mailto:openssl-users@openssl.org">openssl-users@openssl.org</a>> wrote:<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt">Yeah, of course, sorry for the typo. I’ve already found a solution that seems to be working by using EVP_PKEY_get_raw_public_key() for these types of curves. I was confused why it’s not working with EC_KEY
interfaces though it’s type of elliptic curve. Then I found somewhere that it’s implemented outside the context of EC. It’s not clear to me why but I believe there’s a good reason for it.
<o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt"><span style="font-size:11.0pt">Anyway, thanks for your answer!<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt">Regards<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt">Matt<o:p></o:p></span></p>
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<br>
<o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt"><span style="font-size:11.0pt">On 18. 11. 2022, at 17:13, Kyle Hamilton <<a href="mailto:aerowolf@gmail.com" target="_blank">aerowolf@gmail.com</a>> wrote:<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt"> <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt">X25519?<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt">On Mon, Nov 14, 2022, 05:23 ORNEST Matej - Contractor via openssl-users <<a href="mailto:openssl-users@openssl.org" target="_blank">openssl-users@openssl.org</a>> wrote:<o:p></o:p></span></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US" style="font-size:11.0pt">Hi all,</span><span style="font-size:11.0pt"><o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US" style="font-size:11.0pt"> </span><span style="font-size:11.0pt"><o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US" style="font-size:11.0pt">I need to implement support for X52219/X448 for DH key exchange (and Ed52219/Ed448 for DSA) elliptic curves in our project. I need to
export public key for DH exchange in form of DER encoded chunk in form tag+X-coordinate+Y-coordinate. Thus I need to get EC_POINT from EVP_PKEY and encode it as needed. I understand that those key types differs from EC types in way that I need just X coordinate
and a flag bit to reconstruct the key, but still, how do I get the X coordinate?</span><span style="font-size:11.0pt"><o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US" style="font-size:11.0pt">My solution works for all other EC types such as SecpX and Brainpool families, but not for X52219/X448 keys and I do not completely understand
why. Specifically when I decode public key previously encoded with i2d_PUBKEY() to EVP_PEKY and try to get EC_KEY by calling EVP_PKEY_get0_EC_KEY(), it returns NULL and issues an error that it’s not an EC key…</span><span style="font-size:11.0pt"><o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US" style="font-size:11.0pt"> </span><span style="font-size:11.0pt"><o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US" style="font-size:11.0pt">I’m using following code:</span><span style="font-size:11.0pt"><o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US" style="font-size:11.0pt"> </span><span style="font-size:11.0pt"><o:p></o:p></span></p>
<p>EVP_PKEY *key = <span lang="EN-US">… // Decode from DER encoded public key</span><o:p></o:p></p>
<p> <o:p></o:p></p>
<p> if(key != nil) {<o:p></o:p></p>
<p> <o:p></o:p></p>
<p> EC_KEY *ecKey = EVP_PKEY_get0_EC_KEY(key);<o:p></o:p></p>
<p> <span lang="EN-US">/// When X52219 or X448 key is passed, ecKey is NULL</span><o:p></o:p></p>
<p> if(ecKey != NULL) {<o:p></o:p></p>
<p> const EC_POINT *point = EC_KEY_get0_public_key(ecKey);<o:p></o:p></p>
<p> const EC_GROUP *group = EC_KEY_get0_group(ecKey);<o:p></o:p></p>
<p> <o:p></o:p></p>
<p> if(point != NULL && group != NULL) {<o:p></o:p></p>
<p> BIGNUM *bnX = BN_new();<o:p></o:p></p>
<p> BIGNUM *bnY = BN_new();<o:p></o:p></p>
<p> <o:p></o:p></p>
<p> if(EC_POINT_get_affine_coordinates(group, point, bnX, bnY, NULL)) {<o:p></o:p></p>
<p> char *hexX = BN_bn2hex(bnX);<o:p></o:p></p>
<p> char *hexY = BN_bn2hex(bnY);<o:p></o:p></p>
<p> <o:p></o:p></p>
<p> <span lang="EN-US">// Convert to custom data structures</span><o:p></o:p></p>
<p><span lang="EN-US"> …</span><o:p></o:p></p>
<p> }<o:p></o:p></p>
<p> <o:p></o:p></p>
<p> BN_free(bnX);<o:p></o:p></p>
<p> BN_free(bnY);<o:p></o:p></p>
<p> }<o:p></o:p></p>
<p> }<o:p></o:p></p>
<p> }<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US" style="font-size:11.0pt"> </span><span style="font-size:11.0pt"><o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US" style="font-size:11.0pt"> </span><span style="font-size:11.0pt"><o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US" style="font-size:11.0pt">Is there any way how to export those key types in desired format? I’m using OpenSSL version 1.1.1q.</span><span style="font-size:11.0pt"><o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US" style="font-size:11.0pt"> </span><span style="font-size:11.0pt"><o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US" style="font-size:11.0pt">Thank you very much for any hint</span><span style="font-size:11.0pt"><o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US" style="font-size:11.0pt">Matt</span><span style="font-size:11.0pt"><o:p></o:p></span></p>
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