CryptUtil

This Java library provides simple-to-use routines for everyday cryptography tasks.

It does target limited environments (such as for use in an app updater) and as such tries to minimize dependencies (currently: JDK8 only).

Currently implemented utilities:

• Read keys/certificates stored in PKCS8 format, PEM encoded, optionally protected with password
• Create digests (checksums) using strong cryptographic algorithms (like SHA256/SHA512)
• Sign files/digests using strong cryptographic algorithms (like SHA256/SHA256 with RSA)
• verify these signatures

Usage

Maven-Dependency

<dependency>
	<groupId>ch.dvbern.oss.cryptutil</groupId>
	<artifactId>cryptutil</artifactId>
	<version>${cryptutil.version}</version>
</dependency>

HowTo

Create a cryptographically strong digest/checksum using DigestEngine

byte digestBytes[] = new DigestEngine().digestSHA256(is, null);
// openssl compatible: hex-encoding, lowercase
String hexText = DatatypeConverter.printHexBinary(digestBytes).toLowerCase(Locale.US);

Or wrapping an InputStream:

MessageDigest messageDigest = new DigestEngine().configureSHA256(null);
DigestInputStream wrapped = new DigestInputStream(inputStream, messageDigest);
// ... do your stream processing here

byte digestBytes[] = wrapped..getMessageDigest().digest()
// openssl compatible: hex-encoding, lowercase
String hexText = DatatypeConverter.printHexBinary(digestBytes).toLowerCase(Locale.US);

Read Keys/Certificates stored in a PKCS#8 PEM file using PKCS8PEM

// read public key/certificate
RSAPublicKey publicKey = new PKCS8PEM().readCertFromPKCS8EncodedPEM(privateKeyURL.openStream());

// read password protected private key
RSAPrivateKey privateKey = new PKCS8PEM().readKeyFromPKCS8EncodedPEM(privateKeyURL.openStream(), "asdffdsa".toCharArray());

Create a cryptographically strong file signature on a digest and verify it using SignatureEngine

// read private key
RSAPrivateKey privateKey = ... see example above

// create digest
byte digestBytes[] = ... see example above
ByteArrayInputStream digestByteStream = new ByteArrayInputStream(digestBytes);

// sign digest
@NonNull byte[] signatureBytes = new SignatureEngine().signSHA256RSA(privateKey, digestByteStream, null);
writeToFile(signatureBytes, "path/to/signed-digest.bin");

// verify
RSAPublicKey publicKey = ... seeeExample above

byte digestBytes[] = ... see DigestEngine example above
InputStream digestByteStream = new ByteArrayInputStream(digestBytes);

byte signatureBytes[] = readFromFile("path/to/signed-digest.bin");
@NonNull boolean verified = new SignatureEngine().verifySHA256RSA(publicKey, digestByteStream, signatureBytes, null);

Useful information

The following information is also used to generate data for use in unit tests.

Generate an keypair using OpenSSL

First, create the RSA private key using 4096 bits (do not omit the password!):

openssl genrsa -out mykey.pem 4096

Java (i.e.: this library) needs the certificate in PKCS#8 format, so convert it:

openssl pkcs8 -topk8 -inform PEM -in mykey.pem -out mykey-pkcs8.pem

Now generate a public key:

openssl rsa -in mykey.pem -pubout > mykey.pub

Generate signed digests and verify them using OpenSSL

Taken from: Stackoverflow: openssl-command-line-to-verify-the-signature

Generated a RSA signed SHA256 digest using our private key:

openssl dgst -sha256 -sign mykey.pem -out foo.txt.sha256.signed foo.txt 

Verify this digest using our public key:

openssl dgst -sha256 -verify mykey.pub -signature foo.txt.sha256.signed foo.txt
=> Verified OK

Release

See comments in pom.xml for more details.

Built With

• Maven - Dependency Management
• Love :)

Contributing Guidelines

Please read CONTRIBUTING.md for the process for submitting pull requests to us.

Code of Conduct

One healthy social atmospehere is very important to us, wherefore we rate our Code of Conduct high. For details check the file CODE_OF_CONDUCT.md

Authors

• DV Bern AG, Christoph Linder - Initial work - dvbern

See also the list of contributors who participated in this project.

License

This project is licensed under the Apache 2.0 License - see the LICENSE.md file for details.

References

Significant changes

2.0.0 #2: passwords passed in as strings

Strings might get (explicitly or accidentally) interned and thus last longer in memory than expected.

This is clearly unwanted behavior.

Since having backwards compatibility would expose unsafe behavior, breaking the cryptutil API (change passwords from String to char[]) is the only way.

When upgrading from 1.x to 2.x of cryptutil, we recommend to migrate your code to use char[] for passwords, too!

If you cannot do this: just use "yourPassword".toCharArray() when passing the password argument.