Hash functions must be "registered" by import _ "whatever"
. The're not linked into your binary automagically. Actually, nothing not explicitly (or transitively) imported is. However, if you use some non imported entity directly, the compiler/linker will complain. Hash functions, OTOH, as well as some other parts of the stdlib, use a kind of late binding via the Hash interface.
(09:25) jnml@fsc-r550:~/src/tmp/SO/17986762$ cat main.go
package main
import (
"fmt"
"log"
"os"
"code.google.com/p/go.crypto/openpgp"
"code.google.com/p/go.crypto/openpgp/armor"
_ "code.google.com/p/go.crypto/ripemd160"
)
func main() {
to, err := openpgp.NewEntity("John Smith", "comment", "john@example.com", nil)
if err != nil {
log.Fatal(err)
}
from, err := openpgp.NewEntity("John Smith", "comment", "john@example.com", nil)
if err != nil {
log.Fatal(err)
}
recipients := []*openpgp.Entity{to}
armorer, err := armor.Encode(os.Stdout, "PGP MESSAGE", nil)
if err != nil {
log.Fatal(err)
}
defer armorer.Close()
encrypter, err := openpgp.Encrypt(armorer, recipients, from, nil, nil)
if err != nil {
log.Fatal(err)
}
defer encrypter.Close()
fmt.Fprintf(encrypter, "Hello! How are you?")
}
(09:25) jnml@fsc-r550:~/src/tmp/SO/17986762$ go run main.go
-----BEGIN PGP MESSAGE-----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=
=wWmw
-----END PGP MESSAGE-----(09:26) jnml@fsc-r550:~/src/tmp/SO/17986762$