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Cryptography material conversion and verification commands
  1. Introduction
  2. Standards
  3. Common combinations
  4. Conversion
  5. Verification/Inspection
  6. Tips for recognising


It happens that there are many standards for storing cryptography materials (key, certificate, ...) and it isn't always obvious to know which standard is used by just looking at file name extension or file content. There are bunch of questions on stackoverflow asking about how to convert from PEM to PKCS#8 or PKCS#12, while many tried to answer the questions, those answers may not help because the correct answer depends on the content inside the PEM file. That is, a PEM file can contain many different things, such as an X509 certificate, a PKCS#1 or PKCS#8 private key. The worst-case scenario is that someone just store a non-PEM content in "something.pem" file.

When working with cryptography material, I usually follow the 3 steps below:

  • Inspect what format the material is in
  • Understand what format it is required for (for example: logstash server need a PKCS#8 keystore for TLS communication)
  • Convert the material

This gist contains my own understanding about different cryptography standards and their uses, so it's surely imperfect. Feel free to contact me for any improvement.



Standards Content format File encoding Possible content
X509 X Certificates
PKCS#1 X RSA keys (public/private)
PKCS#7 X Certificates, CRLs
PKCS#8 X Private keys, encrypted private keys
PKCS#12 X Certificates, CRLs, private keys
JKS X Certificates, private keys

Common combinations

Some formatted contents are not written into file directly as a binary stream. They are first encoded using encoding rules before writing to file. Below is the list of common combinations of content format and encoding rules:

Content \ Encoding PEM (*) DER (**) Binary
X509 X X
PKCS#7 (***) X X
PKCS#12 (***) X
JKS (***) X

(*) You can concatenate multiple PEM files into a big PEM that contains multiple materials, such as a complete certificate chain.

(**) You can’t simply concatenate DER file to create single DER file → final file may not be readable by other software. If you need to store multiple materials, check (*) or (***).

(***) These formats are designed to store multiple materials.


Conversion Command
PKCS#1 → PKCS#8 openssl pkcs8 -in key_pk1.pem -topk8 -out key_pk8.pem
PKCS#8 → PKCS#1 openssl pkcs8 -in key_pk8.pem -traditional -nocrypt -out key_pk1.pem
openssl rsa -in key_pk8.pem -out key_pk1.pem
X509 → PKCS#7 openssl crl2pkcs7 -nocrl -certfile certificate_x509.pem -out certificate.p7b
PKCS#7 → X509 openssl pkcs7 -print_certs -in certificate.p7b -out certificate_x509.pem
X509 PEM → DER (*) openssl x509 -in certificate_x509.pem -outform DER -out certificate_x509.der
PKCS#1/8 → PKCS#12 openssl pkcs12 -export -nocerts -inkey key.pem -out keystore.p12
PKCS#1/8 + X509 → PKCS#12 openssl pkcs12 -export -inkey key.pem -in cert.pem -out keystore.p12
PKCS#12 → PKCS#8 (**) openssl pkcs12 -info -in keystore.p12 -nodes -nocerts -out key_pk8.pem
PKCS#12 → JKS keytool -importkeystore -srckeystore keystore.p12 -srcstoretype PKCS12 -destkeystore keystore.jks -deststoretype JKS
JKS → PKCS#12 keytool -importkeystore -srckeystore keystore.jks -srcstoretype JKS -destkeystore keystore.p12 -deststoretype PKCS12
JKS → X509 PEM keytool -list -keystore keystore.jks -rfc -alias alias
X509 PEM → JKS keytool -import -alias alias -keystore keystore.jks -file certificate.pem

(*) Similar commands can be used to convert other file (PKCS#1, PKCS#7, PKCS#8) from PEM encoding to DER encoding and vice versa → just need to use the right engine, e.g. x509 for X509, rsa for PKCS#1, …

(**) Only for extracting private key, the output keys are not encrypted. Remove ‘-nodes’ to encrypt output keys.


Content Command
X509 openssl x509 -text -in certificate_x509.cer
openssl x509 -text -in certificate_x509.der -inform DER
PKCS#1 openssl rsa -text -in key_pk1.pem
openssl rsa -text -in key_pk1.der -inform DER
PKCS#7 openssl pkcs7 -text -in certificate.p7b
openssl pkcs7 -text -in certificate_p7.der -inform DER
PKCS#8 openssl pkcs8 -in key_pk8.key -nocrypt
openssl pkcs8 -in key_pk8.der -nocrypt -inform DER
PKCS#12 openssl pkcs12 -info -in keystore.p12
keytool -list -keystore keystore.p12
JKS keytool -list -keystore keystore.jks

Tips for recognising

Content What to look for
PEM-encoded content • Text file starts with “-----BEGIN …” and ends with “… END …-----”.
• File extensions (hopefully): *.pem, *.crt, *.key
PKCS#7/PEM -----BEGIN PKCS7-----
• File extensions: *.p7, *.p7a, *.p7b, *.p7c
PKCS#12 File extensions: *.p12, *.pfx
JKS File extension: *.jks
DER File extensions: *.der, *.cer

Note: Use the right file extension when saving your content into file, but don't rely on file extension when reading, use verification/inspection commands whenever possile.

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