Unable to Read RSA Key

Question

I need to read in an RSA private key from a file to sign a JWT. I am using the openssl to generate a private key. When decrypting the private key getting length too large error

openssl genrsa -des3 -out jwt-private.pem 2048

func main() {

  penbhytes := `-----BEGIN RSA PRIVATE KEY-----
    Proc-Type: 4,ENCRYPTED
    DEK-Info: DES-EDE3-CBC,A30B805A7CC6454D
    
    AOrhSmQZSXu1EjxeJzYlFy2nz6ScUPDqCXEnupExzqFsIFxT4EaJaT+PYSzjVfIq
    RwVfzUxPpAUJ1Ch++s+0tKpKrCaPQdNJthMH1mYEb7WCH8wzVmU473Tlw/jKzrNm
    BzVei4YT+xRi15+etlv0uuXBGcKcMDD13LQS5qfIrEJI6Eei0LGtKqL++eZDt/Nz
    +5R7JP07R0BCXaK+4b+op1mpbbSuxoHTJBkSqd2Aqp4uCyNNGHmm6bBlBuItUYeK
    DAGkUK0iqjUTtiCNsuSr0L288BFZj/y4t2b5gydeaZguVTFYta5TcDTHbZ+R7/yH
    cx8GeijKzYsLoNfE3BIypNMBBClQJfSgumwky1couZTIh18ik8wQySvtbMo5zav+
    zIRrbaGuGY3pInE5zE7k2okilgVnnjBzCQQOxwgXEp5pysRU06CmjbGtt66FvuoE
    KNDhsHJJX1g8LkqivjVOo2ueBrmLItBJh5fS2gPQIVR7hFj3UcYLH/qY0sVqY7aR
    Nf3g0RsUSJWWnJShdoI4zzQNFoZcaTvbbfQc45n1BBNwxmMDNGUL0xQFiioPiiSm
    D1I01jQarKnBvSgWzK81XiaHkRC25Ni1vMjdZATsXpfjao0q1YPzqchdegW1N8rR
    97JZQzirbxV4n0opupX7fs3Xqlnk9SVhr1nHdYMpia0MFfnhhoUiKLAlIzuGJqz6
    5245JgJ2edecuZQ1SM2HrvLSnmq93b4OUafZrCo6vBZiw0EXFPA/BUfz9+PtFzH2
    CQ4MAeJFs0L8bdPA5XVpyA6p8wTIgmKYT64TOFIzaBCtkJcDBnlNKrEZ/Qu7PUbq
    Miz7uQSXBGOI5myEYR0GUhLGbImQz+RpkwNygunjFgBgC7IGFzUfEYpguaUloFPm
    Xgc8/1C6XStluW7f8h7b/K/+U3sCpHKzJdvQz7rptuhs6wtvPVLJse1Ja8E0CnN6
    7S/frRILd9Wal1sRrrZM7fRNYUXCM/3Fz72W55Vp3oKzas4ziBywUvg4LWC4R4yr
    31pJms+fyjAxTX3eSuBsdLGrtWKxxri+oUYooR6oDAiVCVT9llZwXuOcaPzH7A2x
    AbA+g/6t3Qx+zNZ9aMKrBTvsaRThW9AU6Dn9P2X7lyRtR/WMHf+R72vfcNfaGyu6
    Komn4kXhbDdIMvEVSlAF3lSnA1KE/0B3vWEO8q2Vxp66/OCArzX21hUjJr21JT7U
    7YJ6hHQOpdQoZA+2G7Gef1FTiyKYWN9c0UmAdiaKATwwZtu17/lT8oWRZfkp3sUz
    tPLJ08GD91mWq3ExsjTUGWTKAQSp+SDTEJ0SFEw/CH2dhSY/q03eM4cNawVdfDEM
    +50NwHzCiiddLGDASFxKbtkLXZa4xxhg5GTv2F9ObXzKPisM7ipTBC52/EvLU1vP
    Rg92CUoBES2JEhS3M6f0hWdFjKMFaMsdOXKyEzytg31bSPDw0BoKV9a7LKSWhsUk
    7U+gxl84sDUwEZ6jRqRnOrt9gR4FC/m3Z/Fv8KYy1dgyIO2vlprXfHAxlxRWnBAh
    SfTAKja37lLgaMY84EBxsXKayMhWfGIKAb5WABjZcQcdntV2tIVtZjmZPeP/NA57
    -----END RSA PRIVATE KEY-----`

    //using below code to decrypt the private key

    data, _ := pem.Decode([]byte(pembytes))
    privateKeyImported, err := x509.ParsePKCS1PrivateKey(data.Bytes)
    if err != nil {
        fmt.Println(err)
        os.Exit(1)
    }
}

Getting error as length too large

There is a whitespace before the first dash: -----BEGIN RSA PRIVATE KEY----- — Jens
– Jens, Commented Jun 17, 2021 at 6:33
@Jens it's nothing to do with space. it's copy paste mistake, still facing the same issue — user1844634
– user1844634, Commented Jun 17, 2021 at 6:36
The key says it's encrypted, have you tried using x509.DecryptPEMBlock and then use that output when parsing the key? — Simon S.
– Simon S., Commented Jun 17, 2021 at 6:40
The code above does not work. Can you please provide an example that reproduces the error you are describing? play.golang.org/p/4nJOHR9kkJm. — Jens
– Jens, Commented Jun 17, 2021 at 6:41

Simon S. · Accepted Answer · 2021-06-17 06:57:10Z

7

The key says it's encrypted, Proc-Type: 4,ENCRYPTED so you must first decrypt it with the password you entered when generating the key.

data, _ := pem.Decode([]byte(pembytes))
if data == nil {
    log.Fatalf("bad key data, not PEM-encoded?")
}

pemBytes, err := x509.DecryptPEMBlock(data, []byte("somePassword"))
if err != nil {
    log.Fatalf("failed to decrypt block: %v", err)
}

privateKeyImported, err := x509.ParsePKCS1PrivateKey(pemBytes)
if err != nil {
    log.Fatalf("failed to parse private key: %v", err)
}

answered Jun 17, 2021 at 6:57

Simon S.

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