Develop Reference

How to generate PKCS#7 signature from digest?

I want to sign the pdf using pdf digest. I have created the hash using below code,
byte[] buffer = new byte[1024];
int numOfBytesRead =0;
MessageDigest md = null;
md = MessageDigest.getInstance("SHA256","BC");
while((numOfBytesRead = content.read(buffer)) != -1 ){
md.update(buffer, 0, numOfBytesRead);
}
byte[] digest = md.digest();
At the end I need to attach this signature to my pdf. I have found one solution Create pkcs7 signature from file digest, but the algorithm used in the link is SHA256withRSA. My privatekey is genearted using EC algorithm and I need to use SHA256withECDSA.Is it possible to just sign the Hash using SHA256withECDSA and attach the signature to the pdf using PDFBox ExternalSigning Interface.

There are several situations in which Adobe calls a signer's certificate invalid even though apparently it is valid; in the case at hand in particular:
Key usage or Extended key usage values not appropriate
PAdES signature misses an ESS signing-certificate-v2 attribute
Key usage or Extended key usage values not appropriate
This is based on the information the OP first published as an answer
I tried below code still the pdf says Signature is invalid. Can you please check the code,
[...]
I have attached the pdf . Pdf file created
Indeed, Adobe Reader says the signature is invalid, but look more closely:
It says "Document has not been modified since this signature was applied" - This means that the signature is mathematically correct!
The issue is that the "Signer's certificate is invalid", and the reason for this can be seen when digging into the signature property dialogues:
Thus, the problem is that your signer certificate is Not valid for usage.
This is due to the highlighted attribute, while the Key Usage Digital Signature is ok, the "Extended key usage" 1.3.6.1.5.5.8.2.2 (OID for IPSEC Protection) is not!
According to the Adobe Digital Signatures Guide for IT, Adobe Acrobat accepts only
one or more of the following Key usage values (if any)
nonRepudiation
signTransaction (11.0.09 only)
digitalSignature (11.0.10 and later)
and one or more of the following Extended key usage values (if any)
emailProtection
codeSigning
anyExtendedKeyUsage
1.2.840.113583.1.1.5 (Adobe Authentic Documents Trust)
Due to its IPSEC Protection extended key usage value, therefore, your certificate is not considered valid for signing PDF documents.
This probably only is an issue in legacy ISO 32000-1 signatures, probably not in PAdES signatures.
PAdES signature misses an ESS signing-certificate-v2 attribute
This is based on the information the OP first published as an answer
I have created 2 pdf files, PDFA is signed using the digest of the pdf content with below code,
[...]
PDFA
PDFB is created with the same private key and certificate, but instead of digest I am using pdf document content directly which gives me valid signed pdf, PDFB code below,
[...]
PDFB
I think something is missing in the signing part of PDFA which I couldn't figure out.
Here the main difference is not whether you explicitly calculate the hash yourself or allow it to be calculated implicitly, the main difference is that the signature in PDFB includes an ESS signing-certificate-v2 attribute while the one in PDFA does not. This attribute is generated between
//PAdES - PDF Advanced Electronic Signature
and
//PAdES-end
As the comments already hint, this is only necessary for PAdES signatures, not for legacy ISO 32000-1 ones. The answer the OP took his original code from referred to creating a legacy ISO 32000-1 signature (and, therefore, works alright) while the OP creates a PAdES signature.
The presence of an ESS signing certificate attribute is required by the PAdES specification ETSI EN 319 142-1:
e) Generators shall use either the signing certificate or the signing-certificate v2 attribute, depending on the hash function, in accordance with ETSI EN 319 122-1.
(ETSI EN 319 142-1, section 6.3 PAdES baseline signatures)
It references the CAdES specification ETSI EN 319 122-1 which in turn requires
h) Requirement for SPO: ESS signing-certificate. The ESS signing-certificate attribute shall be used if the SHA-1 hash algorithm is used.
i) Requirement for SPO: ESS signing-certificate-v2. The ESS signing-certificate-v2 attribute shall be used when another hash algorithms than SHA-1 is used.
(ETSI EN 319 122-1, section 6.3 Requirements on components and services)

I tried below code still the pdf says Signature is invalid. Can you please check the code,
System.out.println("Hash Signing started");
List<Certificate> certList = getFormatCertificate(strCertificate);
PrivateKey privateKey;
CMSSignedData s = null;
Security.addProvider(new BouncyCastleProvider());
byte[] signature = null;
try {
privateKey = loadPrivateKey(strPrivatekey);
byte[] buffer = new byte[1024];
int numOfBytesRead =0;
MessageDigest md = null;
md = MessageDigest.getInstance("SHA256","BC");
while((numOfBytesRead = content.read(buffer)) != -1 ){
md.update(buffer, 0, numOfBytesRead);
}
byte[] digest = md.digest();
// Separate signature container creation step
JcaCertStore certs = new JcaCertStore(certList);
CMSSignedDataGenerator gen = new CMSSignedDataGenerator();
Attribute attr = new Attribute(CMSAttributes.messageDigest,
new DERSet(new DEROctetString(digest)));
ASN1EncodableVector v = new ASN1EncodableVector();
v.add(attr);
SignerInfoGeneratorBuilder builder = new SignerInfoGeneratorBuilder(new BcDigestCalculatorProvider())
.setSignedAttributeGenerator(new DefaultSignedAttributeTableGenerator(new AttributeTable(v)));
//AlgorithmIdentifier sha256withECDSA = new DefaultSignatureAlgorithmIdentifierFinder().find(signerAlgorithm);
CertificateFactory certFactory = CertificateFactory.getInstance("X.509");
InputStream in = new ByteArrayInputStream(certList.get(certList.size()-1).getEncoded());
X509Certificate cert = (X509Certificate) certFactory.generateCertificate(in);
gen.addSignerInfoGenerator(builder.build(
new JcaContentSignerBuilder(signerAlgorithm).build(privateKey),
new JcaX509CertificateHolder(cert)));
//DErse
// gen.addSignerInfoGenerator(builder.build(
// new JcaContentSignerBuilder(sha256withRSA,
// new DefaultDigestAlgorithmIdentifierFinder().find(sha256withRSA))
// .build(PrivateKeyFactory.createKey(privateKey.getEncoded())),
// new JcaX509CertificateHolder(cert)));
gen.addCertificates(certs);
s = gen.generate(new CMSAbsentContent(), false);
System.out.println("Hash sign completed");
signature = s.getEncoded();// ConstructEcdsaSigValue(s.getEncoded());
} catch (GeneralSecurityException e) {
// TODO Auto-generated catch block
e.printStackTrace();
System.out.println("GeneralSecurityException ::"+e.toString());
} catch (OperatorCreationException e) {
// TODO Auto-generated catch block
e.printStackTrace();
System.out.println("OperatorCreationException ::"+e.toString());
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
System.out.println("IOException ::"+e.toString());
} catch (CMSException e) {
// TODO Auto-generated catch block
e.printStackTrace();
System.out.println("CMSException ::"+e.toString());
}finally{
return signature;
}
I have attached the pdf . Pdf file created
#Mkl/Tilman : I have created 2 pdf files, PDFA is signed using the digest of the pdf content with below code,
System.out.println("Hash Signing started");
List<Certificate> certList = getFormatCertificate(strCertificate);
PrivateKey privateKey;
CMSSignedData s = null;
Security.addProvider(new BouncyCastleProvider());
byte[] signature = null;
try {
privateKey = loadPrivateKey(strPrivatekey);
/*byte[] buffer = new byte[1024];
int numOfBytesRead =0;
MessageDigest md = null;
//md = MessageDigest.getInstance("SHA256","BC");
md = MessageDigest.getInstance("SHA-256");
while((numOfBytesRead = content.read(buffer)) != -1 ){
md.update(buffer, 0, numOfBytesRead);
}
byte[] digest = md.digest();*/
MessageDigest md = MessageDigest.getInstance("SHA256", "BC");
byte[] digest = md.digest(IOUtils.toByteArray(content));
// Separate signature container creation step
JcaCertStore certs = new JcaCertStore(certList);
CMSSignedDataGenerator gen = new CMSSignedDataGenerator();
Attribute attr = new Attribute(CMSAttributes.messageDigest,
new DERSet(new DEROctetString(digest)));
ASN1EncodableVector v = new ASN1EncodableVector();
v.add(attr);
SignerInfoGeneratorBuilder builder = new SignerInfoGeneratorBuilder(new BcDigestCalculatorProvider())
.setSignedAttributeGenerator(new DefaultSignedAttributeTableGenerator(new AttributeTable(v)));
//AlgorithmIdentifier sha256withECDSA = new DefaultSignatureAlgorithmIdentifierFinder().find(signerAlgorithm);
CertificateFactory certFactory = CertificateFactory.getInstance("X.509");
InputStream in = new ByteArrayInputStream(certList.get(certList.size()-1).getEncoded());
X509Certificate cert = (X509Certificate) certFactory.generateCertificate(in);
gen.addSignerInfoGenerator(builder.build(
new JcaContentSignerBuilder(signerAlgorithm).build(privateKey),
new JcaX509CertificateHolder(cert)));
//DErse
// gen.addSignerInfoGenerator(builder.build(
// new JcaContentSignerBuilder(sha256withRSA,
// new DefaultDigestAlgorithmIdentifierFinder().find(sha256withRSA))
// .build(PrivateKeyFactory.createKey(privateKey.getEncoded())),
// new JcaX509CertificateHolder(cert)));
gen.addCertificates(certs);
s = gen.generate(new CMSAbsentContent(), false);
System.out.println("Hash sign completed");
signature = s.getEncoded();// ConstructEcdsaSigValue(s.getEncoded());
} catch (GeneralSecurityException e) {
// TODO Auto-generated catch block
e.printStackTrace();
System.out.println("GeneralSecurityException ::"+e.toString());
} catch (OperatorCreationException e) {
// TODO Auto-generated catch block
e.printStackTrace();
System.out.println("OperatorCreationException ::"+e.toString());
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
System.out.println("IOException ::"+e.toString());
} catch (CMSException e) {
// TODO Auto-generated catch block
e.printStackTrace();
System.out.println("CMSException ::"+e.toString());
}finally{
return signature;
}
PDFA
PDFB is created with the same private key and certificate, but instead of digest I am using pdf document content directly which gives me valid signed pdf, PDFB code below,
SignatureInterface signatureInterface = new SignatureInterface() {
#SuppressWarnings("rawtypes")
#Override
public byte[] sign(InputStream content) throws IOException {
try {
byte[] certificateByte = null;
Store certs = new JcaCertStore(certificates);
//PAdES - PDF Advanced Electronic Signature
//ESS - Enhanced Security Services
//ASN1 - Abstract Syntax Notation One-standard interface description language for defining data structures that can be serialized and deserialized in a cross-platform way
// Generating certificate hash
MessageDigest md = MessageDigest.getInstance("SHA-256");
md.update(certificates.get(certificates.size()-1).getEncoded());
byte[] certHash = md.digest();
// Generating certificate hash ends
System.out.println("Cert hash generated");
//ESSCertIDv2 identifies the certificate from the hash
ESSCertIDv2 essCert1 =
new ESSCertIDv2(new AlgorithmIdentifier(NISTObjectIdentifiers.id_sha256), certHash);
ESSCertIDv2[] essCert1Arr =
{
essCert1
};
SigningCertificateV2 scv2 = new SigningCertificateV2(essCert1Arr);
Attribute certHAttribute =
new Attribute(PKCSObjectIdentifiers.id_aa_signingCertificateV2, new DERSet(scv2));
ASN1EncodableVector v = new ASN1EncodableVector();
v.add(certHAttribute);
AttributeTable at = new AttributeTable(v);
//Create a standard attribute table from the passed in parameters - certhash
CMSAttributeTableGenerator attrGen = new DefaultSignedAttributeTableGenerator(at){
protected Hashtable createStandardAttributeTable(Map parameters)
{
Hashtable result = super.createStandardAttributeTable(parameters);
result.remove(CMSAttributes.signingTime);
return result;
}
};
//PAdES-end
System.out.println("CMSAttributeTableGenerator generated");
SignerInfoGeneratorBuilder genBuild =
new SignerInfoGeneratorBuilder(new BcDigestCalculatorProvider());
genBuild.setSignedAttributeGenerator(attrGen);
//Get single certificate
org.spongycastle.asn1.x509.Certificate certas1 = org.spongycastle.asn1.x509.Certificate.getInstance(ASN1Primitive.fromByteArray(certificates.get(certificates.size()-1).getEncoded()));
// ContentSigner interface creates SHA256withECDSA signer using PvtKey
ContentSigner sha1Signer = new JcaContentSignerBuilder(signerAlgorithm).build(privateKey);
//Creates SignerInfoGenerator using X.509 cert and ContentSigner
SignerInfoGenerator sifGen = genBuild.build(sha1Signer, new X509CertificateHolder(certas1));
// CMSSignedDataGenerator generates a pkcs7-signature message
CMSSignedDataGenerator gen = new CMSSignedDataGenerator();
gen.addCertificates(certs);
gen.addSignerInfoGenerator(sifGen);
//Creates CMS message from PDF
CMSProcessableInputStream msg = new CMSProcessableInputStream(content);
//Generate a CMS Signed Data object which can be carrying a detached CMS signature
//msg - content to be signed
CMSSignedData signedData = gen.generate(msg, false);
System.out.println("CMSSignedData is done");
return signedData.getEncoded();
} catch (GeneralSecurityException e) {
throw new IOException(e);
} catch (CMSException e) {
throw new IOException(e);
} catch (OperatorCreationException e) {
throw new IOException(e);
}
}
};
System.out.println("CMSSignedData is done2");
PDDocument pdDocument = PDDocument.load(inputfile);
System.out.println("pdDocument loaded");
pdDocument.addSignature(signature, signatureInterface);
PDFB
I think something is missing in the signing part of PDFA which I couldn't figure out.

Android Fingerprint invalidation

I'm playing around with the Fingerprint demo for Android, in particular the invalidation scenarios, but need a little help to translate this into production worthy logic.
I've tested the app and get the initCipher to fail due to invalidation after adding a fingerprint, but the app has to be running and the key generated while you change the settings. This is because the demo generates a new key each time the app starts. In reality you wouldn't want to do this, but instead generate the key if doesn't exist and reuse it if it does to enforce proper invalidation whether the app is running or not.
How can you modify the app so that the key isn't generated each time, but instead a check to see if one exists first is performed, then that key loaded subsequently? Can you then remove the key once invalidated so the previous logic and enrolment cycle applies?

Found the answer on my own by looking at the KeyStore class a bit more and modifying initCipher(). Not the best implementation, but good enough to test out stuff:
private boolean initCipher(Cipher cipher, String keyName) {
try {
mKeyStore.load(null);
// ADDED: Check is keystore contains my key name
if(!mKeyStore.containsAlias(DEFAULT_KEY_NAME)) {
// ADDED: Create if it doesn't
createKey(DEFAULT_KEY_NAME, true);
}
SecretKey key = (SecretKey) mKeyStore.getKey(keyName, null);
cipher.init(Cipher.ENCRYPT_MODE, key);
return true;
} catch (KeyPermanentlyInvalidatedException e) {
// ADDED: Remove the key if it is invalidated so
// it can be created fresh next time
try {
mKeyStore.deleteEntry(keyName);
} catch (KeyStoreException e1) {
e1.printStackTrace();
return false;
}
return false;
} catch (KeyStoreException | CertificateException | UnrecoverableKeyException | IOException
| NoSuchAlgorithmException | InvalidKeyException e) {
throw new RuntimeException("Failed to init Cipher", e);
}
}
Also need to remove the createKey() call from onCreate() too obviously.

Issue with Robolectric with cipher in android application

Hi I am using Robolectric for test cases. I am facing some issue while simulating for encryption relateed test cases. I tried to use cipher with AES for encryption. And it is giving me some error. I tried it in following manner :
#Test
public void testGet() {
Cipher cipher = null;
try {
SecretKey sks= getKeySpec(pass, salt);
cipher = Cipher.getInstance("AES");
cipher.init(Cipher.DECRYPT_MODE, sks);
} catch (NoSuchAlgorithmException e) {
e.printStackTrace();
} catch (NoSuchPaddingException e) {
e.printStackTrace();
} catch (InvalidKeySpecException e) {
e.printStackTrace();
} catch (InvalidKeyException e) {
e.printStackTrace();
}
}
public SecretKey getKeySpec(char[] pass, byte[] salt) throws NoSuchAlgorithmException, InvalidKeySpecException {
//generate key spec...
return secretKeyFactory.generateSecret(keySpec);
}
It gives me following error :
Illegal key size or default parameters
I already added JCE for illegal size exception. It is working if I run it on device and properly working in my application. Only thing when I try with robolectric it is giving me this error.Need some help. Thank you.

The reason behind this is Robolectric runs on JVM. JVM supports up to 128 bit key encryption only. Therefore if you are using 256 bit key encryption you need to use Java Cryptography Extension (JCE). follow this answer to how to do that

Android fingerprint on SDK<23

I have a project on Android with minSDK=17 and targetSDK=23. We have a fingerprint authentication in this project made using FingerprintManager class (it was added in SDK23). We added SDK version check, so we are not using anything related to fingerprint if SDK<23. But in older SDK versions app behaviour is unpredictable: on some versions app just crashing, on other -- fingerprint not working (so, it's ok).
My question:
1) Is it any good and easy-to-implement libraries for minSDK=17, that can recognize fingerprints?
2) How can I avoid app crashing in devices with SDK<23?
Crash error:
E/dalvikvm: Could not find class 'android.hardware.fingerprint.FingerprintManager', referenced from method nl.intratuin.LoginActivity.loginByFingerprint
E/AndroidRuntime: FATAL EXCEPTION: main java.lang.VerifyError:
LoginActivity at java.lang.Class.newInstanceImpl(Native Method)
Some new info: created HelloWorld fingerprint project using this tutorial:
http://www.techotopia.com/index.php/An_Android_Fingerprint_Authentication_Tutorial
Found the root of the problem:
FingerprintDemoActivity->cipherInit:
try {
keyStore.load(null);
SecretKey key = (SecretKey) keyStore.getKey(KEY_NAME,
null);
cipher.init(Cipher.ENCRYPT_MODE, key);
return true;
} catch (KeyPermanentlyInvalidatedException e) {
return false;
} catch (KeyStoreException | CertificateException
| UnrecoverableKeyException | IOException
| NoSuchAlgorithmException | InvalidKeyException e) {
throw new RuntimeException("Failed to init Cipher", e);
}
First catch block breacking whole app with error I mentioned above. Of course, I can just remove this catch (this exception extends InvalidKeyException, so it will be handled), and return false in case of any exceptions. Is it any better way?

I think, I found acceptable solution: catch not KeyPermanentlyInvalidatedException, but InvalidKeyException. Everything working fine this way. Still have no idea how this exception crashed whole app...

It happened to me also..even when i used : if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M).. my app crashes on android 4.4- kitkat. so eventually the problem was in the initCipher method in the catches part - see the following code (even though i m not suppose to get there as it targeted to M and above... very strange behaviour..) :
#TargetApi(Build.VERSION_CODES.M)
private boolean initCipher() {
try {
mKeyStore.load(null);
SecretKey key = (SecretKey) mKeyStore.getKey(KEY_NAME, null);
mCipher.init(Cipher.ENCRYPT_MODE, key);
return true;
} catch (KeyStoreException | CertificateException | UnrecoverableKeyException | IOException
| NoSuchAlgorithmException e) {
throw new RuntimeException("Failed to init Cipher", e);
} catch (InvalidKeyException e) {
e.printStackTrace();
return false;
}
}
apparently the order off the catches matter..so just make sure to write it as i mentioned.

Reason for Crash:
The FingerprintManager class works with Android version 23 and Higher.
If your app is using FingerprintManager class and runs on older version of Android then you will encounter this exception.
Supporting older versions of Android:
Use FingerprintManagerCompat instead of FingerprintManager if you are planning to support Android <23. The FingerprintManagerCompat class internally checks for the Android version and handle Authentication part with ease.
How to Use it:
Replace android.hardware.fingerprint.FingerprintManager With android.support.v4.hardware.fingerprint.FingerprintManagerCompat
Replace android.os.CancellationSignal With android.support.v4.os.CancellationSignal
See Sample Code
https://github.com/hiteshsahu/FingerPrint-Authentication-With-React-Native-Android/blob/master/android/app/src/main/java/com/aproject/view/Fragments/FingerprintAuthenticationDialogFragment.java

Have a look at a library created by afollestad called digitus.
This library can fall back to a password if fingerprints are not available.
Any devices prior to SDK 23 need to use their own separate device manufacturer based sdk.

just follow android studio hint, it will be OK.
try {
mKeyStore.load(null);
SecretKey key = (SecretKey) mKeyStore.getKey(keyName, null);
cipher.init(Cipher.ENCRYPT_MODE, key);
return true;
} catch (IOException | NoSuchAlgorithmException | CertificateException
| UnrecoverableKeyException | KeyStoreException | InvalidKeyException e) {
e.printStackTrace();
throw new RuntimeException("Failed to init Cipher", e);
}

To answer the second part of the question
How can I avoid app crashing in devices with SDK<23?
This simplistic logic check will suffice:
if (Build.VERSION.SDK_INT < 23) {
// Handle the mechanism where the SDK is older.
}else{
// Handle the mechanism where the SDK is 23 or later.
}

I solved this by moving all the fingerprint code to a helper class so that the classes related to the fingerprint code are not imported in the activity and by instantiating the helper class only when the SDK_INT is greater than 23 (In my case, as I'm supporting only Android 6+)

I also had this problem.Even when i used : if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M).. my app crashes on lower API's. I solved that as follow:
Replaced these codes:
try {
keyStore.load(null);
SecretKey key = (SecretKey) keyStore.getKey(KEY_NAME,
null);
cipher.init(Cipher.ENCRYPT_MODE, key);
return true;
} catch (KeyPermanentlyInvalidatedException e) {
return false;
} catch (KeyStoreException | CertificateException
| UnrecoverableKeyException | IOException
| NoSuchAlgorithmException | InvalidKeyException e) {
throw new RuntimeException("Failed to init Cipher", e);
}
with:
try {
keyStore.load(null);
} catch (CertificateException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} catch (NoSuchAlgorithmException e) {
e.printStackTrace();
}
SecretKey key = null;
try {
key = (SecretKey) keyStore.getKey(KEY_NAME,
null);
} catch (KeyStoreException e) {
e.printStackTrace();
} catch (NoSuchAlgorithmException e) {
e.printStackTrace();
} catch (UnrecoverableKeyException e) {
e.printStackTrace();
}
try {
cipher.init(Cipher.ENCRYPT_MODE, key);
} catch (InvalidKeyException e) {
e.printStackTrace();
}
return true;

Android - Encode & Decode RSA with Private Key?

I am trying to encode and decode Strings on Android using a Private Key generated and stored using the Android Key Store Provider that was introduced in Android 4.3
I can successfully generate and get the private key using the following code:
private void generatePrivateKey(Activity context, String alias){
/** Generate a new entry in the KeyStore by using the * KeyPairGenerator API. We have to specify the attributes for a * self-signed X.509 certificate here so the KeyStore can attach * the public key part to it. It can be replaced later with a * certificate signed by a Certificate Authority (CA) if needed. */
Calendar cal = Calendar.getInstance();
Date now = cal.getTime();
cal.add(Calendar.YEAR, 1);
Date end = cal.getTime();
KeyPairGenerator kpg = null;
try {
kpg = KeyPairGenerator.getInstance("RSA", "AndroidKeyStore");
} catch (NoSuchAlgorithmException e) {
e.printStackTrace();
} catch (NoSuchProviderException e) {
e.printStackTrace();
}
try {
kpg.initialize(new KeyPairGeneratorSpec.Builder(context)
.setAlias(alias)
.setStartDate(now)
.setEndDate(end)
.setSerialNumber(BigInteger.valueOf(1))
.setSubject(new X500Principal("CN=" + alias))
.build());
} catch (InvalidAlgorithmParameterException e) {
e.printStackTrace();
}
KeyPair kp = kpg.generateKeyPair();
/*
* Load the Android KeyStore instance using the the
* "AndroidKeyStore" provider to list out what entries are
* currently stored.
*/
KeyStore ks = null;
try {
ks = KeyStore.getInstance("AndroidKeyStore");
ks.load(null);
Enumeration<String> aliases = ks.aliases();
} catch (KeyStoreException e) {
e.printStackTrace();
} catch (CertificateException e) {
e.printStackTrace();
} catch (NoSuchAlgorithmException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
/*
* Use a PrivateKey in the KeyStore to create a signature over
* some data.
*/
KeyStore.Entry entry = null;
try {
entry = ks.getEntry(alias, null);
} catch (NoSuchAlgorithmException e) {
e.printStackTrace();
} catch (UnrecoverableEntryException e) {
e.printStackTrace();
} catch (KeyStoreException e) {
e.printStackTrace();
}
if (!(entry instanceof KeyStore.PrivateKeyEntry)) {
Log.w("E", "Not an instance of a PrivateKeyEntry");
}
else{
Log.w("E", "Got Key!");
privateKeyEntry = ((KeyStore.PrivateKeyEntry) entry).getPrivateKey();
}
}
And here is the code I am using for encrypt (encode) and decrypt (decode):
private String encryptString(String value){
byte[] encodedBytes = null;
try {
Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding", "AndroidOpenSSL");
cipher.init(Cipher.ENCRYPT_MODE, privateKeyEntry );
encodedBytes = cipher.doFinal(value.getBytes());
} catch (Exception e) {
e.printStackTrace();
}
return Base64.encodeToString(encodedBytes, Base64.DEFAULT);
}
private String decryptString(String value){
byte[] decodedBytes = null;
try {
Cipher c = Cipher.getInstance("RSA/ECB/PKCS1Padding", "AndroidOpenSSL");
c.init(Cipher.DECRYPT_MODE, privateKeyEntry );
decodedBytes = c.doFinal(Base64.decode(value, Base64.DEFAULT));
} catch (Exception e) {
e.printStackTrace();
}
return new String(decodedBytes);
}
The Encryption appears to work fine but when I try to decrypt it I get the following error:
javax.crypto.BadPaddingException: error:0407106B:rsa routines:RSA_padding_check_PKCS1_type_2:block type is not 02
Googling this seems to suggest that the private key used for decryption is different to the one used for decryption but in my code I use the exact same private key for both. I have also seen it suggested to set the key size manually but doing this in the KeyPairGenerator builder like this:
.setKeySize(1024);
Did not work and seems to be only available on API 19, I need to target API 18.
Can anyone help point me in the right direction as to a solution?

You are not using the public key for encryption.
When you are using asymmetric encryption algorithms, you need to use the public key to encrypt your data, and the private key only to decrypt it again.
Besides encryption, you can also use the private key for signing, but that's not what you want here, so let's forget about that for the moment.
If you take the public key from the generated pair, when you encrypt your string, and the private key when decrypting, you should get the desired result. The public key you can extract by accessing the certificate from the keystore-object that holds your private key.
Alternatively you could also use a symmetric algorithm like AES and by that make your work a lot easier. Plus, symmetric algorithms are usually much faster, which is why asymmetric algorithms are never used purely, but in conjunction with symmetric algorithms, building so-called hybrid algorithms.

Signature generation is not the same thing as encryption. You need to encrypt with the public key and decrypt with the private key if you want encryption. If you want signature generation, you need to sign with the private key and verify with the public key. This order cannot be reversed nor can it be mixed (securely).