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June 19, 2010

Generate a .jks keystore using .key and .crt files

Filed under: * Security — streethawkz @ 7:16 pm

Generate a .jks keystore using .key and .crt files :

Notes :

x509 standard assumes a strict hierarchical system of certificate authorities (CAs) for issuing the certificates.

Structure of a certificate :

The structure of an X.509 v3 digital certificate is as follows:

Serial Number
Algorithm ID
Not Before
Not After
Subject Public Key Info
Public Key Algorithm
Subject Public Key
Issuer Unique Identifier (Optional)
Subject Unique Identifier (Optional)
Extensions (Optional)

Certificate Signature Algorithm
Certificate Signature

Issuer and subject unique identifiers were introduced in Version 2, Extensions in Version 3. Nevertheless, the Serial number must be unique for each certificate issued by a specific CA

Certificate filename extensions :

Common filename extensions for X.509 certificates are:

.pem – (Privacy Enhanced Mail) Base64 encoded DER certificate, enclosed between “—–BEGIN CERTIFICATE—–” and “—–END CERTIFICATE—–”

.cer, .crt, .der – usually in binary DER form, but Base64-encoded certificates are common too (see .pem above)

.p7b, .p7c – PKCS#7 SignedData structure without data, just certificate(s) or CRL(s)

.p12 – PKCS#12, may contain certificate(s) (public) and private keys (password protected)

.pfx – PFX, predecessor of PKCS#12 (usually contains data in PKCS#12 format, e.g, with PFX files generated in IIS)

PKCS#7 is a standard for signing or encrypting (officially called “enveloping”) data. Since the certificate is needed to verify signed data, it is possible to include them in the SignedData structure. A .P7C file is a degenerated SignedData structure, without any data to sign.
PKCS#12 evolved from the PFX (Personal inFormation eXchange) standard and is used to exchange public and private objects in a single file.

Steps :

Tools like in F5 load balancers generate .crt and .key files ( they basically use openssl ).

Here .crt is the signed certificate from a CA and key contains the private key.

These keys and certificates are in PEM format.

– Open both the files in a notepad and copy the contents in it to a new notepad file and save it with extension .pem

– Now we need to convert this .pem to .des

Note : DES is a binary format and non readable whereas PEM are in human readable form.
Note : Make sure OpenSSL is installed ( You can download it from : )

– You can use the following command to convert PEM to DER format.

Command : openssl pkcs8 -topk8 -nocrypt -in key.pem -inform PEM -out key.der -outform DER ( this command will convert the key file (PEM format) containing private key to DER format )

Command : openssl x509 -in cert.pem -inform PEM -out cert.der -outform DER ( This command converts the signed certificate (PEM format) to DER format ).

– Now we need to add the signed certificate and the private key into the keystore.

Keytool does not let you import an existing private key for which you already have a certificate.

– Download and compile the java code from the link below :

Link : ( )

Command : javac

The above code will add the private key and the certificate into a .jks keystore.

Default name of the keystore that will be created : keystore.ImportKey ( you can edit the code and change it to identity.jks )

Default password/passphrase for the private key : importkey ( you can edit the code to make changes in it accordingly )

Default alias name given to this key would be : importkey

Once you have the .class file run the command below to generate the keystore ( i.e identity.jks ) :

Command :  java ImportKey key.der cert.der ( Note the first argument is the key file and the second is the cerificate (both in DER format) )

Note : The keystore is not created in the same directory. You can find it in the root folder ( Eg : C:\Documents and Settings\CoolDragon\… )

– Now import your rootca.crt file into this keystore to complete the chaining of certificates

Command : keytool -import -file rootca.crt -alias -trustcacerts -keystore keystore.ImportKey -storepass importkey

– Now list the certificates of the keystore to check if the chaining is fine :

Command : keytool -v -list -keystore keystore.ImportKey -storepass importkey

Identity.jks file is now ready 🙂



  1. Thanks for the nice tutorial. Was having some issues in importing private key that was created using openssl, to a keystore format.

    Comment by Yuva Kumar — February 3, 2011 @ 3:07 pm

  2. Hi, nice article.

    Does it to possible import chain of certificates using this method?

    Comment by victar — November 22, 2011 @ 8:09 pm

  3. yes you should be able to import a cert chain as well..

    Comment by streethawkz — November 22, 2011 @ 10:47 pm

  4. Thank you for sharing this article. This was of great help for me.

    Comment by Shradha — February 8, 2013 @ 2:00 pm

  5. Try these steps.. it is much simpler 🙂

    Below are the steps to import a crt and private key to a keystore :

    1) Copy the crt contents from your email to a notepad and save this file with .pem extension.

    Eg : cert.pem

    Contents :













    2) Copy the contents of private key from your email and save it into a notepad with .pem extension.

    Eg : key.pem

    Contents :






    Run the following command :

    java utils.ImportPrivateKey -keystore identity.jks -storepass password -keyfile mykey -keyfilepass password -certfile certs.pem -keyfile key.pem -alias mykey

    Sample output :

    d:\Oracle\Middleware1036\user_projects\domains\wild_card_certificate_domain\certificates>java utils.ImportPrivateKey -keystore identity.jks -storepass password -keyfile mykey -keyfilepass password -certfile cert.pem -keyfile key.pem -alias mykey

    No password was specified for the key entry
    Key file password will be used

    Imported private key key.pem and certificate cert.pem
    into a new keystore identity.jks of type jks under alias mykey

    Comment by streethawkz — July 17, 2013 @ 1:55 am

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