sk-usbhid: preserve UV requirement for resident keys - #701
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savely-krasovsky wants to merge 1 commit into
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sk-usbhid: preserve UV requirement for resident keys#701savely-krasovsky wants to merge 1 commit into
savely-krasovsky wants to merge 1 commit into
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When loading resident credentials, derive SSH_SK_USER_VERIFICATION_REQD directly from the credential's credProtect policy. The previous code only preserved the flag when the authenticator did not report the uv capability. As a result, UV_REQUIRED credentials downloaded from authenticators with built-in UV were saved with flags 0x21 instead of 0x25. Do not make preservation of the credential policy depend on the authenticator's current UV capability. Keep compatibility with libfido2 versions without fido_cred_prot().
savely-krasovsky
marked this pull request as ready for review
July 25, 2026 18:44
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What changed
Derive
SSH_SK_USER_VERIFICATION_REQDdirectly from a resident credential'scredProtectpolicy when loading it from an authenticator.Why
Resident credentials created with
verify-requiredstoreFIDO_CRED_PROT_UV_REQUIREDon the authenticator.During
ssh-keygen -Kandssh-add -K,read_rks()currently propagates this asSSH_SK_USER_VERIFICATION_REQDonly when the authenticator does not report itsuvcapability. Authenticators with built-in UV therefore produce downloaded key files with flags0x21instead of
0x25.The credential policy should be preserved independently of the authenticator's current UV capability. The compatibility guard ensures that builds using libfido2 versions without
fido_cred_prot()retaintheir existing behavior.
Validation
--with-security-key-builtinandlibfido2 1.16.
UV_OPTIONAL_WITH_ID(0x02) downloaded with OpenSSH flags0x21.UV_REQUIRED(0x03) downloaded with OpenSSH flags0x25.0x25.