“This is the sixth day of my participation in the August More Text Challenge.

An overview of

The Security library provides implementations of Security best practices related to reading and writing static data and key creation and validation.

The library uses builder mode to provide security defaults for the following security levels:

  • Strong security balancing reliable encryption with good performance This level of security applies to consumer applications such as banking applications and chat applications, as well as enterprise applications that perform certificate revocation checks.
  • Maximum security This security level applies to hardware – supported key stores and applications that require user intervention to provide key access.

The secret key management

  • The Security library can use multiple sets of secret keys and can encrypt files and SP. The secret key set is stored in sp
  • The primary key is stored in the system key library

Security encryption operation

Rely on

Using the Security library requires importing the following dependencies

implementation("Androidx. Security: security - crypto: 1.0.0")
    implementation("Androidx. Security: the security identity - the credential: 1.0.0 - alpha02")
    implementation("Androidx. Security: security - app - the authenticator: 1.0.0 - alpha02")
    androidTestImplementation("Androidx. Security: security - app - the authenticator: 1.0.0 - alpha01")
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Existing problems

The minimum API version supported by the Security library is 24. We have the following two solutions:

  • Manifest declared in the < USES – SDK tools: overrideLibrary = “androidx. Security. Identity. The credential, androidx. Security” / >

  • Upgrade the minimum API version to 24, but this will require adaptation for both above and below API24

Use Security to encrypt files

Write encrypted data

Unable to repeat write

To repeatedly write data to a file that already existsopenFileOutputMethod throws an exception because the write cannot be repeated. See comment:

Write data:

  1. code

  • The encryptedFile. Builder in this example takes the longest to build, 300-600ms on my phone, so try not to use encryption for non-sensitive files

  • There’s also a lot of data bloat stored in files, which means more storage space is taken up

val encrypt = EncryptedFile.Builder(
                    getFile("Anandzhuo write file encrypted data.txt").apply {
                        if (exists()) {// Delete the file if it already exists
                            delete()
                        }
                    },
                    this@MainActivity."Write a random key.",
                    EncryptedFile.FileEncryptionScheme.AES256_GCM_HKDF_4KB
                ).build()
                startRecord()
                encrypt.openFileOutput().apply {
                    write("Write whatever dot string you want".toByteArray(charset = Charsets.UTF_8))
                    flush()
                    close()
                }

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  1. The effect

Read encrypted data

Val encrypt = encryptedFile. Builder(getFile(" encrypt "), this@MainActivity, "write a key", EncryptedFile.FileEncryptionScheme.AES256_GCM_HKDF_4KB ).build() startRecord() val bytes = BufferedInputStream(encrypt.openFileInput()).readBytes() val result = String(bytes, charset = Charsets.UTF_8)Copy the code

Use Security to encrypt SharePreference

The Security library provides EncryptedSharedPreferences to encrypt the key – value of deposited in the sp

But the well-known sp is a pit dad, so still should only apply EncryptedSharedPreferences on sensitive data is stored

Write data to Shar

share = EncryptedSharedPreferences.create( "encryptdata", "key", this@MainActivity, EncryptedSharedPreferences.PrefKeyEncryptionScheme.AES256_SIV, EncryptedSharedPreferences.PrefValueEncryptionScheme.AES256_GCM ) share.edit().let { it.putString("key", "SharePreference data ") it. Apply ()}Copy the code

Read data from SharePreference

share = EncryptedSharedPreferences.create(
            "encryptdata",
            "key",
            this@MainActivity,
            EncryptedSharedPreferences.PrefKeyEncryptionScheme.AES256_SIV,
            EncryptedSharedPreferences.PrefValueEncryptionScheme.AES256_GCM
        )
val value = share.getString("key", "")
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