decrypt with public key

How can I decrypt a message signed with a private key in golang?

$ openssl genrsa -out ./server/server.key
Generating RSA private key, 2048 bit long modulus
..................+++
.............................................+++

$ openssl rsa -in ./server/server.key -pubout -out ./client/client.pub
writing RSA key

$ echo "secret" | openssl rsautl -inkey ./server/server.key -sign > ./secret

# decrypt with public key
$ openssl rsautl -inkey ./client/client.pub -pubin -in ./secret
secret

I fully understood my question, it was about RSA_public_decrypt method of openssl: https://www.openssl.org/docs/man1.1.0/crypto/RSA_public_decrypt.html

I did not found any pure-golang realization. Realization with cgo: https://github.com/dgkang/rsa/blob/master/rsa/rsa.go

UPD, work for me:

func RSA_public_decrypt(pubKey *rsa.PublicKey, data []byte) []byte {
    c := new(big.Int)
    m := new(big.Int)
    m.SetBytes(data)
    e := big.NewInt(int64(pubKey.E))
    c.Exp(m, e, pubKey.N)
    out := c.Bytes()
    skip := 0
    for i := 2; i < len(out); i++ {
        if i+1 >= len(out) {
            break
        }
        if out[i] == 0xff && out[i+1] == 0 {
            skip = i + 2
            break
        }
    }
    return out[skip:]
}

I think there is a bit of a misunderstanding here. openssl rsautl -sign does not encrypt the data. It produces a signature. The contents in your secret file is not "secret", encrypted. Rather, it is a signature of the text "secret" that is signed with the private key.

Using the public key, you can -verify the signature, but this isn't really what you are trying to do. It sounds like you want encrypt/decrypt, not sign/verify.

Use the -encrypt and -decrypt options of rsautl. Encryption happens with the public key, and decryption happens with the private key.

Keep in mind there are limits to the amount of data you can encrypt with RSA. Typically, you would protect a symmetric key with RSA, and use the symmetric key to do bulk encryption and decryption.