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openssl: check key type for sk-ecdsa in ossl_key_from_openssh() - #2672
abdul-khaliq-khalid wants to merge 5 commits into
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The sk-ecdsa branch was the only one not matching `want_method`, so `ssh2_rsa_new_priv()`, `ssh2_dsa_new_priv()` and `ssh2_ed25519_new_priv()` accepted an OpenSSH sk-ecdsa private key and returned an EC key as their context. With OpenSSL 1.1.1 and forks the `EC_KEY` pointer was then used as `RSA`/`DSA`. Add the same check the sk-ssh-ed25519 branch uses, and a test.
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| "aXN0cDI1NgAAAEEEaxfR8uEsQkf4vOblY6RA8ncDfYEt6zOg9KE5RdiYwpZP\n" | ||
| "40Li/hp/m47n60p8D54WK84zV2sxXs7LtkBoN79R9QAAAARzc2g6AQAAABCq\n" | ||
| "qqqqqqqqqqqqqqqqqqqqAAAAAAAAAAABAgME\n" | ||
| "-----END OPENSSH PRIVATE KEY-----\n"; |
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Can you add a comment documenting the ssh-keygen command used
to generate this key? Or, could we perhaps use an existing key from
the keys/ subdir? If there is no fitting one there, maybe add a new one?
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ssh-keygen -t ecdsa-sk -b 256 -N '' -m RFC4716 -C 'id_ecdsa_openssh_sk' -f 'keys/id_ecdsa_openssh_sk' # empty commentThis one produces some extra stuff at the end of the blob with my test key at least.
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Nothing in keys/ fit, so I've added keys/id_ecdsa_openssh_sk (plus .pub and the Makefile.inc entries) using your command in keys-generate.sh, and the test now embeds that key with a comment pointing back to it. The old blob was hand-built with just a 16-byte handle and empty reserved/comment fields, which is why yours had more at the end. I don't have a FIDO token at hand, so this one was made with OpenSSH's regress/misc/sk-dummy provider (SSH_SK_PROVIDER), which means its key handle is a dummy PEM blob rather than an opaque one. Feel free to regenerate it with a real token if you'd prefer. The test still fails without the fix and passes with it.
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Nice! No intent to generate it with my hw key. Which key do you think would
be better, the shorter one you included in the C file, or the new one with PEM
EC key embedded in it?
That key could be loaded with ssh2_file_to_blob() in test_simple.c. I guess
it'd would also need srcdir_path() from session_fixture.c to locate it on disk.
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I'd go with the ssh-keygen one. It's reproducible from keys-generate.sh, while the short one was hand-assembled with fake handle/reserved fields. The PEM blob in the handle only comes from sk-dummy, but the parser treats the handle as opaque, so for this test that doesn't matter.
Switched the test to read keys/id_ecdsa_openssh_sk via ssh2_file_to_blob() + srcdir_path(), which also gets rid of the embedded string and the overlength pragmas. It still fails without the fix and passes with it.
Add keys/id_ecdsa_openssh_sk with its keys-generate.sh line and embed it in the test instead of the hand-crafted blob.
Read keys/id_ecdsa_openssh_sk with `ssh2_file_to_blob()` and `srcdir_path()` instead of embedding it, which also drops the -Woverlength-strings pragmas.
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| QUUzQmRrWGVPdlBHdGY3WjNLS3ovQ1FycXpQL3QvV1ZzeFh2dkMrbDFiWFlLTGY5Q3ZQaz | ||
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| UklWQVRFIEtFWS0tLS0tCgAAAAAAAAATaWRfZWNkc2Ffb3BlbnNzaF9zawECAwQFBg== |
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Thanks for the update, it's looking good, but I wonder if there is
somewhere a public, trusted, test key we could use here?
This one is special because we cannot generate it via keys-generate.sh,
and I couldn't positively confirm that using someone's actual key here
is safe to use either. So were at the situation of uploading a blob to the
repo, one that we cannot reproduce or replace with a fresh one.
I looked the openssh code you mentioned, it built a static lib, but could
not make it work to generate an actual key.
If this is unsolvable, I'm fine with merging this without a test.
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OpenSSH's own regress suite has one: regress/unittests/sshkey/testdata/ecdsa_sk1, generated by their mktestdata.sh with the sk-dummy provider (ssh-keygen -w "$SK_DUMMY" -t ecdsa-sk -C "ECDSA-SK test key #1" -N "" -f ecdsa_sk1). It has been in openssh-portable unchanged since 2020, so it has a public origin and no one's real credential is involved.
I've swapped keys/id_ecdsa_openssh_sk for that key, and keys-generate.sh now fetches it from a pinned openssh-portable commit instead of calling ssh-keygen, so the script keeps working and the blob can be re-fetched from a known source. The test still fails without the fix and passes with it.
If you'd still rather land this without the test, I'm fine dropping it.
Replace the locally generated sk-dummy key with ecdsa_sk1 from OpenSSH's regress/unittests/sshkey/testdata, which has a public origin and a documented generation command, and fetch it in keys-generate.sh from a pinned openssh-portable commit so it can be reproduced.
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In
ossl_key_from_openssh()thesk-ecdsa-sha2-nistp256@openssh.combranch is the only one that does not checkwant_method, sossh2_rsa_new_priv(),ssh2_dsa_new_priv()andssh2_ed25519_new_priv()accept an OpenSSH sk-ecdsa private key and return an EC key as their context. With OpenSSL 1.1.1/LibreSSL/BoringSSL/AWS-LC that context is anRSA *orDSA *, so theEC_KEY *ends up inRSA_size()/RSA_sign()/RSA_free(); it is reachable vialibssh2_userauth_publickey_frommemory()/_fromfile()with anssh-rsaorssh-dsspublic key paired with such a private key (on OpenSSL 3 the call just returns anEVP_PKEYof type EC). The fix adds the same check thesk-ssh-ed25519branch has;ssh2_pub_privkey()andssh2_sk_pubkey()still load sk-ecdsa keys, and the new test in test_simple fails without it. I checked open and closed PRs and found none covering this branch.