Using RSA/ECB/OAEPPadding algorithm for encryption key not working in android

Question

When I use the RSA/ECB/OAEPPadding algorithm in the encryption method below, an error gets thrown in Android:

Error:javax.crypto.IllegalBlockSizeException: error:04000072:RSA routines:OPENSSL_internal:DATA_TOO_LARGE_FOR_KEY_SIZE
      javax.crypto.IllegalBlockSizeException: error:04000072:RSA routines:OPENSSL_internal:DATA_TOO_LARGE_FOR_KEY_SIZE.

Before this, I was using the RSA/ECB/PKCS1Padding algorithm. After the switch to the RSA/ECB/OAEPPadding algorithm, I am getting the above exception, however, the codebase did not change.

I tried using this code:

Key key = ...;
Cipher cipher = Cipher.getInstance("RSA/ECB/OAEPPadding");
// To use SHA-256 the main digest and SHA-1 as the MGF1 digest
cipher.init(Cipher.ENCRYPT_MODE, key, new OAEPParameterSpec("SHA-256", "MGF1", MGF1ParameterSpec.SHA1, PSource.PSpecified.DEFAULT));
// To use SHA-256 for both digests
cipher.init(Cipher.ENCRYPT_MODE, key, new OAEPParameterSpec("SHA-256", "MGF1", MGF1ParameterSpec.SHA256, PSource.PSpecified.DEFAULT));

but I get this error:

CryptoHelper: Error:javax.crypto.BadPaddingException: error:0400007e:RSA routines:OPENSSL_internal:KEY_SIZE_TOO_SMALL
    javax.crypto.BadPaddingException: error:0400007e:RSA routines:OPENSSL_internal:KEY_SIZE_TOO_SMALL

Any help is appreciated!

Alex Zab · Accepted Answer · 2025-07-30 06:39:40Z

-1

Cipher cipher = Cipher.getInstance("RSA/ECB/OAEPPadding");
// To use SHA-256 the main digest and SHA-1 as the MGF1 digest
cipher.init(Cipher.ENCRYPT_MODE, key, new OAEPParameterSpec("SHA-256", "MGF1", MGF1ParameterSpec.SHA1, PSource.PSpecified.DEFAULT));
// To use SHA-256 for both digests

This code is working fine

edited Jul 30 at 6:39

Alex Zab

326 bronze badges

answered Jan 12, 2022 at 4:02

Hemavathi

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