How to convert a interface{} into type *rsa.PublicKey golang

Question

I have public key stored in a variable of type interface{}

-----BEGIN PUBLIC KEY-----    MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDdlatRjRjogo3WojgGHFHYLugdUWAY9iR3fy4arWNA1KoS8kVw33cJibXr8bvwUAUparCwlvdbH6dvEOfou0/gCFQsHUfQrSDv+MuSUMAe8jzKE4qW+jK+xQU9a03GUnKHkkle+Q0pX/g6jXZ7r1/xAK5Do2kQ+X5xK9cipRgEKwIDAQAB
-----END PUBLIC KEY-----

Is there anyway I can convert this into type *rsa.PublicKey in golang. It might involve some intermediate step like converting interface{} to string first may be.

Answer 1

In general you would decode a pem file (assuming this is in a x509) cert using the crypto/x509 library. The provided example in the documentation is as follows:

package main

import (
    "crypto/dsa"
    "crypto/ecdsa"
    "crypto/rsa"
    "crypto/x509"
    "encoding/pem"
    "fmt"
)

func main() {
    const pubPEM = `
-----BEGIN PUBLIC KEY-----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-----END PUBLIC KEY-----`

    block, _ := pem.Decode([]byte(pubPEM))
    if block == nil {
        panic("failed to parse PEM block containing the public key")
    }

    pub, err := x509.ParsePKIXPublicKey(block.Bytes)
    if err != nil {
        panic("failed to parse DER encoded public key: " + err.Error())
    }

    switch pub := pub.(type) {
    case *rsa.PublicKey:
        fmt.Println("pub is of type RSA:", pub)
    case *dsa.PublicKey:
        fmt.Println("pub is of type DSA:", pub)
    case *ecdsa.PublicKey:
        fmt.Println("pub is of type ECDSA:", pub)
    default:
        panic("unknown type of public key")
    }
}

I'm not really sure about the encoding you have there though. The following might help you past that hurdle:

• RSA Public Key format