"No DEK-Info header in block" when attempting to read encrypted private key

Question

I'm trying to read an encrypted PKCS8 private key file. I generated the keys like this:

openssl genrsa -out file.pem -passout pass:file -aes256 1024
openssl pkcs8 -topk8 -inform pem -in file.pem -outform pem -out filePKCS8.pem

And I try reading it in Go this way:

block, _ := pem.Decode(key)
return x509.DecryptPEMBlock(block, password)

But I get an error saying:

x509: no DEK-Info header in block

However, I can't figure out what's going wrong. Am I generating the key wrong or am I using the wrong library? I see libraries specifically for reading unencrypted PKCS8 files but none for encrypted PKCS8 files specifically.

Does anyone have any idea?

Answer 1

Go don't have function to decrypt PKCS8 keys in standard library.

You can this package: https://github.com/youmark/pkcs8/blob/master/pkcs8.go#L103

Answer 2

A longer explaination for anyone with the same problem.

What would work

Your first command

openssl genrsa -out file.pem -passout pass:file -aes256 1024

generates a PKCS#1 private key file (file.pem):

-----BEGIN RSA PRIVATE KEY-----
Proc-Type: 4,ENCRYPTED
DEK-Info: AES-256-CBC,1DA219DB746F88C6DDA0D852A0FD3232

AEf09rGkgGEJ79GgO4dEVsArwv4IbbODlxy95uHhfkdGYmuk6OlTpiCUE0GT68wn
KFJfBcHr8Z3VqiHGsXxM5QlKhgnfptxfbrdKErgBD5LQcrvnqmf43KeD4lGQcpiy
...
...
mAKMCwiU/GKZz8ZwQ4qGkBlVVCOFfgwmfbqguJF2l8yzM8lYI9MZ9NEwKkvEbc
-----END RSA PRIVATE KEY-----

This private key file can be parsed and decrypted by x509.DecryptPEMBlock() alright.

What would not work and why

Your second command

openssl pkcs8 -topk8 -inform pem -in file.pem -outform pem -out filePKCS8.pem

converts that file into PKCS#8 format (filePKCS8.pem).

The subcommmand genpkey would directly produce a similar result:

openssl genpkey -algorithm RSA -aes256 \
  -pkeyopt rsa_keygen_bits:1024 -out filePKCS8.pem

The generated filePKCS8.pem (either way) would look similar to this:

-----BEGIN ENCRYPTED PRIVATE KEY-----
MIISrTBXBgkqhkiG9w0BBQ0wSjKpBgkqhkiG9w0BBQwwHAQIKL+ordsVfqsCAggB
MAwGCCqGSIb3DQIJCQAwHQYJYIZIWAUDBAEqBBCipOAAxWkC0/zkNLNYTSMgBIIS
...
...
zfdxjZ0XmPiwED2azsLMnRrWnRj2UqMtnv9zO/ucik9za
-----END ENCRYPTED PRIVATE KEY-----

x509.DecryptPEMBlock() does not support this format. And as specified in #8860, the Go's core library has no real plan to support pkcs#8 in the near future.

As mentioned by Gregory, if you want to work with it, you'll have better luck with 3rd party library like github.com/youmark/pkcs8 (Documentation).