Flutter key store cryptography

This plugin helps you by generating the assymetric RSA key pair.

The keys are generated and persisted in android/ios keystore.

Assymetric Key details

The details of keys generated and store in android/iOS keystore is as follows:

  • type -> RSA
  • signature algorithm -> SHA256withRSA
  • key size -> 2048 bit

Android

  • The RSA key pair is stored android Keystore
  • AES encryption is used.
  • The AES secret is encrypted with RSA and stored in shared preference.
  • For Android 9 (API leverl 28) StrongBox is enabled by default.
  • As keystore is available in Android 4.3 (API level 18) and hgher, hence this is minimum required Android.

iOS

  • The RSA key pair is stored in iOS Keychain
  • This plugin will run on iOS 10.0 and higher

Using plugin

This plugin exposes the following methods:

  • getPublicKey: returns the RSA public key
  • encrypt: encrypts the plain text using private key from the key pair
  • verify: verifies a signature and returns a boolean if the signature is signed by the same key pair.

1) getPublicKey

This function is used to get the RSA public key which is store the android and ios key store. This key pair is persisted in key store, i.e it is generated once, and always re used for signing and verification.

defination

static Future<String> getPublicKey()

usage:

final String rsaPublicKey = await Cipher.getPublicKey();

2) sign

This function returns a signature which is signed by the platoform's private key.

defination

static Future<String> sign(String plainData)

usage:

final String signature = await Cipher.sign('some plain data');

3) verify

This function returns a boolean, and takes a plain data and signature.

This function verifies the signature against the plain data, it returns true if the signature is produced by the same device's private key.

defination

static Future<bool> verify(String plainText, String signature)

usage:

final bool result = await Cipher.verify('somePassword', 'SIGNATURE-XX');

The above will checks if the SIGNATURE-XX matches the somePassword or not.

Libraries

call_method_type_enum
cipher
cipher_utils
exception_message_constant