How to use key pair generated by openpgp in go - go

Question

I'm trying to generate keypair with openpgp lib and when I want to test it by encrypting a test string, it returns the following error openpgp: invalid argument: cannot encrypt because no candidate hash functions are compiled in. (Wanted RIPEMD160 in this case.). However it works when I pass a public key exported from gpg.
Also I'm wondering how to encrypt the private key like gpg --generate-key does?
func main() {
var e *openpgp.Entity
var pubKey *bytes.Buffer
e, _ = openpgp.NewEntity("testUser", "test", "test#test.test", nil)
for _, id := range e.Identities {
err := id.SelfSignature.SignUserId(id.UserId.Id, e.PrimaryKey, e.PrivateKey, nil)
if err != nil {
fmt.Println(err)
return
}
}
buf := new(bytes.Buffer)
w, err := armor.Encode(buf, openpgp.PublicKeyType, nil)
if err != nil {
fmt.Println(err)
return
}
e.Serialize(w)
w.Close()
pubKey = buf
// Encrypting test with public key
entity, err := openpgp.ReadArmoredKeyRing(pubKey)
if err != nil {
fmt.Println(err)
return
}
buf = new(bytes.Buffer)
encoderWriter, err := armor.Encode(buf, "PGP MESSAGE", make(map[string]string))
if err != nil {
fmt.Println(err)
return
}
encryptorWriter, err := openpgp.Encrypt(encoderWriter, entity, nil, nil, nil)
if err != nil {
fmt.Println(err)
return
}
encryptorWriter.Write([]byte("hello world"))
encryptorWriter.Close()
encoderWriter.Close()
fmt.Println(buf.String())
}

Answer 1

I had the exact same error.
TL; DR
It seems that it's an abandoned bug of the golang.org/x/crypto/openpgp package.
golang.org/x/crypto/openpgp package is frozen and deprecated. (= wontfix)
Use a patched fork package instead.
github.com/ProtonMail/go-crypto package # GitHub
TS; DR
Since the official "golang.org/x/crypto/openpgp" package was frozen and deprecated, as long as we use the "golang.org/x/crypto/openpgp" package, it seems that the only current workaround is to either;
Downgrade the Go version and the package, then blank import "_ golang.org/x/crypto/ripemd160" as #mh-cbon mentioned.
Patch the rejected PR on your own. (Rejected due to the freezing of x/crypto/openpgp package)
Patch: https://github.com/golang/crypto/pull/128/files
PR: Use correct default hashes and default ciphers when no preferences given
But I had to implement an OpenPGP key pair generator on Go 1.16.6. Don't ask why...
So, my current alternative was to use the forked package. Which was one of the abounding forks that the Go team mentioned as a sample.
github.com/ProtonMail/go-crypto package # GitHub
go get github.com/ProtonMail/go-crypto
Remove golang.org/x/crypto/openpgp from go.mod
Replace all the "golang.org/x/crypto/openpgp" to "github.com/ProtonMail/go-crypto/openpgp" in the source code.
go mod tidy
References
"x/crypto/openpgp: mark as frozen and deprecated" | Issue #44226 | go | golang # GitHub
"x/crypto/openpgp: new entities cannot be encrypted to by default" | Issue #37646 | go | golang # GitHub
"x/crypto/openpgp: new entities cannot be encrypted to by default" | Issue #12153 | go | golang # GitHub