x/crypto: 4 tests will run into https://pkg.go.dev/crypto/[email protected]#hdr-Minimum_key_size

[dmitshur]

Go 1.24 makes a change to crypto/rsa.GenerateKey that makes it return an error if a key of less than 1024 bits is requested, also adding a GODEBUG rsa1024min for it. See https://go.dev/doc/go1.24#cryptorsapkgcryptorsa.

When x/crypto's go.mod is updated to Go language 1.24 or newer (which will happen this August based on https://go.dev/s/release#timeline and https://go.dev/design/69095-x-repo-continuous-go#why-1_n_1_0), there are 4 tests in x/crypto that will begin to fail:

crypto $ go get [email protected] && go mod tidy && go fix ./... && go test ./...
--- FAIL: TestTLSChallengeCertOpt (0.00s)
    acme_test.go:762: crypto/rsa: 512-bit keys are insecure (see https://go.dev/pkg/crypto/rsa#hdr-Minimum_key_size)
FAIL
FAIL	golang.org/x/crypto/acme	4.133s
--- FAIL: TestCache (0.00s)
    autocert_test.go:624: crypto/rsa: 512-bit keys are insecure (see https://go.dev/pkg/crypto/rsa#hdr-Minimum_key_size)
--- FAIL: TestValidCert (0.00s)
    autocert_test.go:699: crypto/rsa: 512-bit keys are insecure (see https://go.dev/pkg/crypto/rsa#hdr-Minimum_key_size)
FAIL
FAIL	golang.org/x/crypto/acme/autocert	0.334s
--- FAIL: TestValidateCert (0.00s)
    certs_test.go:120: Unable to validate certificate: ssh: certificate signature does not verify
FAIL
FAIL	golang.org/x/crypto/ssh	3.458s
[...]

This is being reported early thanks to a -tiplang builder (see https://ci.chromium.org/ui/p/golang/builders/ci/x_crypto-gotip-linux-amd64-tiplang). It's not causing a problem today since x/crypto/go.mod's go directive is at 1.20, but does need to be fixed at some point, and this is the tracking issue for that.

CC @golang/security.

[gopherbot]

Change https://go.dev/cl/647975 mentions this issue: all: update certs for go1.24

[gopherbot]

Change https://go.dev/cl/648676 mentions this issue: main.star: remove known issues for -tiplang builder in x/crypto, x/tools