proposal: crypto/x509: support extracting X25519 public keys from certificates #70667
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ianlancetaylor
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Proposal-Crypto
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CC @golang/security |
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Per the crypto/x509 package documentation "the primary goal of the package is to provide compatibility with the publicly trusted TLS certificate ecosystem and its policies and constraints". Since X25519 is not supported by TLS, and X25519 keys are not allowed in certificates issued by publicly trusted CAs, per the CABF baseline requirements, I'm not sure there is a strong reason for us to add explicit support for these certificates. As you say, ParseCertificate does parse these certificates. If you do need to use them for whatever purpose, you can still manually extract the key from the Certificate.RawSubjectPublicKeyInfo field and use it for your purposes. This is slightly more complex, but I think a worthwhile trade off to prevent people from accidentally misusing these certificates for purposes they are not intended for. |
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We could probably include an Example for how to use cryptobyte to extract a public key from RawSubjectPublicKeyInfo. |
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That sounds fine to me. That said, I am also interested in generating certificates. It looks like CreateCertificate() doesn’t respect RawSubjectPublicKeyInfo right now. Would it make sense to extend CreateCertificate() to do so? |
Proposal Details
Even though X25519 key pairs (not to be confused with Ed25519 key pairs) can't be used to establish TLS connections, there are still cases in which you want to use them in combination with X.509 certificates. For example, if X25519 is used to perform public key authenticated encryption (e.g., NaCl's crypto_box), X.509 certificates may be used to authenticate the identity of the peer before encrypting/decrypting. RFC 8410 added the ability to embed X25519 public keys into X.509 certificates for such use cases.
Right now
x509.ParseCertificate()completes successfully when presented with a certificate containing an X25519 public key. Unfortunately, it does end up discarding the public key, asCertificate.PublicKeyAlgorithmandCertificate.PublicKeywill be set toUnknownPublicKeyAlgorithmandnil, respectively.The proposal here is to actually let
x509.ParseCertificate()extract the public key from the certificate and return it in the form of an*ecdh.PublicKey. ThePublicKeyAlgorithmenumeration will be extended to include an additional element for this public key algorithm, which will simply be calledX25519.Code changes can be found here: https://go-review.googlesource.com/c/go/+/632875
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