x/crypto/curve25519: consider removing dependency on "fmt" if worthwhile

[dmitshur]

The curve25519 package imports fmt and uses it 3 times:

return nil, fmt.Errorf("bad scalar length: %d, expected %d", l, 32)
return nil, fmt.Errorf("bad point length: %d, expected %d", l, 32)
return nil, fmt.Errorf("bad input point: low order point")

If it makes sense to remove fmt, then the golang.org/x/crypto/curve25519 can be moved in go/build.TestDependencies from:

# CRYPTO-MATH is core bignum-based crypto - no cgo, net; fmt now ok.

To:

# CRYPTO is core crypto algorithms - no cgo, fmt, net.

Similarly to how crypto/ed25519/internal/edwards25519 was moved in CL 276272.

@FiloSottile, do you think doing so would be worthwhile?

[FiloSottile]

Yeah, why not, those can be simple strconv.Itoa and errors.New calls. I'll send a CL.

[dmitshur]

Sounds good. Please include a small test in x/crypto that this package doesn't import fmt, so this property doesn't accidentally regress without the benefit of go/build's test.

[gopherbot]

Change https://golang.org/cl/348069 mentions this issue: x/crypto/curve25519: remove dependency on "fmt"

[aaqaishtyaq]

Hey @FiloSottile, I would like to work on this. I have removed dependency on fmt from curve25519/curve25519.go.
Let me know if I am going right and additional changes I need to make.

Thanks

[ianlancetaylor]

This doesn't seem urgent, moving milestone to Backlog.

[gopherbot]

Change https://go.dev/cl/413794 mentions this issue: go/build: test no fmt import for crypto/curve25519