43 lines
1.8 KiB
Kotlin
43 lines
1.8 KiB
Kotlin
package com.openless.app
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import java.security.GeneralSecurityException
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import javax.crypto.Cipher
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import javax.crypto.SecretKey
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import javax.crypto.spec.GCMParameterSpec
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/** Pure JCA AES-GCM packet codec; AndroidKeyStore ownership lives in the facade. */
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internal object OpenLessCredentialCipher {
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internal const val NONCE_BYTES = 12
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internal const val TAG_BITS = 128
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private const val TAG_BYTES = TAG_BITS / 8
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private const val TRANSFORMATION = "AES/GCM/NoPadding"
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@Throws(GeneralSecurityException::class)
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fun seal(key: SecretKey, plaintext: ByteArray, aad: ByteArray): ByteArray {
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val cipher = Cipher.getInstance(TRANSFORMATION)
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cipher.init(Cipher.ENCRYPT_MODE, key)
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val nonce = cipher.iv
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require(nonce.size == NONCE_BYTES) { "unexpected AES-GCM nonce length" }
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cipher.updateAAD(aad)
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val ciphertext = cipher.doFinal(plaintext)
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return byteArrayOf(nonce.size.toByte()) + nonce + ciphertext
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}
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@Throws(GeneralSecurityException::class)
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fun open(key: SecretKey, packet: ByteArray, aad: ByteArray): ByteArray {
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if (packet.isEmpty()) {
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throw IllegalArgumentException("malformed credential packet")
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}
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val nonceLength = packet[0].toInt() and 0xff
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if (nonceLength != NONCE_BYTES || packet.size < 1 + nonceLength + TAG_BYTES) {
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throw IllegalArgumentException("malformed credential packet")
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}
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val nonce = packet.copyOfRange(1, 1 + nonceLength)
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val ciphertext = packet.copyOfRange(1 + nonceLength, packet.size)
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val cipher = Cipher.getInstance(TRANSFORMATION)
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cipher.init(Cipher.DECRYPT_MODE, key, GCMParameterSpec(TAG_BITS, nonce))
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cipher.updateAAD(aad)
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return cipher.doFinal(ciphertext)
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}
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}
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