Convert PKCS#8 Format Private Key to PKCS#1 using OpenSSL

Private keys are a fundamental component of secure communication, playing an important role in encryption and decryption processes. Private keys can come in different formats; two common ones are PKCS#8 and PKCS#1. This tutorial explains how to convert PKCS#8 format private key to PKCS#1 using OpenSSL.

Let's say we have the following PKCS#8 format private key:

-----BEGIN PRIVATE KEY-----
MIIBVQIBADANBgkqhkiG9w0BAQEFAASCAT8wggE7AgEAAkEA3+i8CaGg06cTZWgl
5S6ekQH4LBPI9sojxWdD6strvmuIG2Z9isZ1QPwK/+n6KgvzrHBK9f4dheeQ998R
dzsiVQIDAQABAkA3eyS0wj7mkvykYPUa371csv86dMCUHixU6qySjkspSGcvdqNQ
UuAfRJ97n8m8wkNSHhF2HIWH2lPdC/MsZX/VAiEA8QLAZXzsUiEIQ04enLZRq0cv
YkD8mLyXVpT56ZrdEDsCIQDt1bMedIH1kCcAvg4PHAugXw1NeJSvpOpUqOyPwmB+
rwIhAJDhq5EW4OWaT+JOAt8IRt4k49o34OFcdcmpsvZ4jy3jAiA7n+2N3wuNspv0
lbEUnKVViT7egzJTbnbIzqivyb1DRQIhAKbr3cYY4mk0HKFQg3oEhWi2stSPulYz
KNkxLcXmqXjr
-----END PRIVATE KEY-----

The command to convert a PKCS#8 formatted private key to PKCS#1 is as follows:

openssl rsa -in test.key -traditional -out test2.key

The meaning of options:

• -in test.key - specifies the input file which contains private key in PKCS#8 format.
• -traditional - instructs that traditional format (PKCS#1) for the output key should be used.
• -out test2.key - specifies the output file which contains converted private key in PKCS#1 format.

Output:

-----BEGIN RSA PRIVATE KEY-----
MIIBOwIBAAJBAN/ovAmhoNOnE2VoJeUunpEB+CwTyPbKI8VnQ+rLa75riBtmfYrG
dUD8Cv/p+ioL86xwSvX+HYXnkPffEXc7IlUCAwEAAQJAN3sktMI+5pL8pGD1Gt+9
XLL/OnTAlB4sVOqsko5LKUhnL3ajUFLgH0Sfe5/JvMJDUh4RdhyFh9pT3QvzLGV/
1QIhAPECwGV87FIhCENOHpy2UatHL2JA/Ji8l1aU+ema3RA7AiEA7dWzHnSB9ZAn
AL4ODxwLoF8NTXiUr6TqVKjsj8Jgfq8CIQCQ4auRFuDlmk/iTgLfCEbeJOPaN+Dh
XHXJqbL2eI8t4wIgO5/tjd8LjbKb9JWxFJylVYk+3oMyU252yM6or8m9Q0UCIQCm
693GGOJpNByhUIN6BIVotrLUj7pWMyjZMS3F5ql46w==
-----END RSA PRIVATE KEY-----

If you ever need to convert a PKCS#1 private key back to PKCS#8, you can use the following OpenSSL command:

openssl rsa -in test2.key -out test.key