CertGuru

Convert a PKCS#1 key to PKCS#8

To convert a PKCS#1 private key to PKCS#8, run `openssl pkcs8 -topk8 -in pkcs1.key -out pkcs8.key -nocrypt`. You can tell the two apart from the header line alone — PKCS#1 reads `-----BEGIN RSA PRIVATE KEY-----` and PKCS#8 reads `-----BEGIN PRIVATE KEY-----`. PKCS#8 wraps the same key material in a structure that also records which algorithm the key belongs to, which is why it works for RSA, EC and Ed25519 alike while PKCS#1 is RSA-only. Java, Go and most modern libraries accept only PKCS#8.

Updated August 19, 2026 Verified against OpenSSL 3.5.7

The command #

PKCS#1 to unencrypted PKCS#8
openssl pkcs8 -topk8 -in pkcs1.key -out pkcs8.key -nocrypt

Replace these values

PlaceholderWhat to put there
-topk8Convert to PKCS#8. Without it the subcommand converts the other way.
-nocryptWrite the output unencrypted. Omit to be prompted for a passphrase.
pkcs1.keyInput starting -----BEGIN RSA PRIVATE KEY-----.
pkcs8.keyOutput starting -----BEGIN PRIVATE KEY-----.

Telling the formats apart # 

head -n1 private.key
Header line Format Algorithms
-----BEGIN RSA PRIVATE KEY----- PKCS#1 RSA only
-----BEGIN EC PRIVATE KEY----- SEC1 EC only
-----BEGIN PRIVATE KEY----- PKCS#8, unencrypted Any
-----BEGIN ENCRYPTED PRIVATE KEY----- PKCS#8, encrypted Any

Producing an encrypted PKCS#8 key #

Encrypt with AES-256 rather than the default
openssl pkcs8 -topk8 -in pkcs1.key -out pkcs8.key -v2 aes-256-cbc

OpenSSL prompts for the passphrase. In a script, add -passout file:/run/secrets/key-password rather than putting the secret on the command line.

Converting an EC key #

The same command works — -topk8 is not RSA-specific despite the format it usually replaces:

openssl pkcs8 -topk8 -in ec-sec1.key -out ec-pkcs8.key -nocrypt

Verify the conversion #

The key must still match its certificate afterwards. Comparing public keys proves the material survived intact:

These two must print the same hash
openssl pkey -in pkcs1.key -pubout | openssl sha256
openssl pkey -in pkcs8.key -pubout | openssl sha256

And confirm the header is what you expected:

head -n1 pkcs8.key
Expected output 
-----BEGIN PRIVATE KEY-----

If it reads BEGIN ENCRYPTED PRIVATE KEY, you left out -nocrypt and a server that cannot prompt for a passphrase will fail to start.

Going the other way #

See convert PKCS#8 to PKCS#1.

Frequently asked questions

How do I tell PKCS#1 from PKCS#8 at a glance?
The header line. -----BEGIN RSA PRIVATE KEY----- is PKCS#1, -----BEGIN PRIVATE KEY----- is unencrypted PKCS#8, and -----BEGIN ENCRYPTED PRIVATE KEY----- is PKCS#8 with a passphrase. -----BEGIN EC PRIVATE KEY----- is the EC equivalent of PKCS#1, defined by SEC1.
Does this change the key?
No. The same private key material is rewrapped in a different ASN.1 structure. The public key, the certificate it matches and every signature it has produced remain valid.
Why does Java reject my key?
Java's KeyFactory reads PKCS#8 only. A BEGIN RSA PRIVATE KEY file will fail to parse no matter how it is loaded, which is the single most common reason to run this conversion.
What if I want the output encrypted?
Drop -nocrypt and OpenSSL prompts for a passphrase, producing a BEGIN ENCRYPTED PRIVATE KEY file. Add -v2 aes-256-cbc to choose the cipher explicitly rather than accepting the default.

References

Related pages