# GCMParameterSpec Added in[API level 19](https://developer.android.com/guide/topics/manifest/uses-sdk-element.html#ApiLevels) # GCMParameterSpec ``` open class GCMParameterSpec : AlgorithmParameterSpec ``` |---|--------------------------------------------------------------------------------------------------------------------------| | [kotlin.Any](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-any/index.html) || | ↳ | [javax.crypto.spec.GCMParameterSpec](https://developer.android.com/reference/kotlin/javax/crypto/spec/GCMParameterSpec#) | Specifies the set of parameters required by a using the Galois/Counter Mode (GCM) mode. Simple block cipher modes (such as CBC) generally require only an initialization vector (such as`IvParameterSpec`), but GCM needs these parameters: - `IV`: Initialization Vector (IV) - `tLen`: length (in bits) of authentication tag T In addition to the parameters described here, other GCM inputs/output (Additional Authenticated Data (AAD), Keys, block ciphers, plain/ciphertext and authentication tags) are handled in the`Cipher`class. Please see[RFC 5116](http://www.ietf.org/rfc/rfc5116.txt)for more information on the Authenticated Encryption with Associated Data (AEAD) algorithm, and[NIST Special Publication 800-38D](http://csrc.nist.gov/publications/nistpubs/800-38D/SP-800-38D.pdf), "NIST Recommendation for Block Cipher Modes of Operation: Galois/Counter Mode (GCM) and GMAC." The GCM specification states that`tLen`may only have the values {128, 120, 112, 104, 96}, or {64, 32} for certain applications. Other values can be specified for this class, but not all CSP implementations will support them. ## Summary | Public constructors || |---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|---| | [GCMParameterSpec](https://developer.android.com/reference/kotlin/javax/crypto/spec/GCMParameterSpec#GCMParameterSpec(kotlin.Int,%20kotlin.ByteArray))`(`tLen:` `[Int](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-int/index.html)`, `src:` `[ByteArray](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-byte-array/index.html)!`)` Constructs a GCMParameterSpec using the specified authentication tag bit-length and IV buffer. | | [GCMParameterSpec](https://developer.android.com/reference/kotlin/javax/crypto/spec/GCMParameterSpec#GCMParameterSpec(kotlin.Int,%20kotlin.ByteArray,%20kotlin.Int,%20kotlin.Int))`(`tLen:` `[Int](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-int/index.html)`, `src:` `[ByteArray](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-byte-array/index.html)!`, `offset:` `[Int](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-int/index.html)`, `len:` `[Int](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-int/index.html)`)` Constructs a GCMParameterSpec object using the specified authentication tag bit-length and a subset of the specified buffer as the IV. | | Public methods || |----------------------------------------------------------------------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------| | open[ByteArray](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-byte-array/index.html)! | [getIV](https://developer.android.com/reference/kotlin/javax/crypto/spec/GCMParameterSpec#getIV())`()` Returns the Initialization Vector (IV). | | open[Int](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-int/index.html) | [getTLen](https://developer.android.com/reference/kotlin/javax/crypto/spec/GCMParameterSpec#getTLen())`()` Returns the authentication tag length. | ## Public constructors ### GCMParameterSpec Added in[API level 19](https://developer.android.com/guide/topics/manifest/uses-sdk-element.html#ApiLevels) ``` GCMParameterSpec(     tLen: Int,     src: ByteArray!) ``` Constructs a GCMParameterSpec using the specified authentication tag bit-length and IV buffer. | Parameters || |--------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | `tLen` | [Int](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-int/index.html):the authentication tag length (in bits) | | `src` | [ByteArray](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-byte-array/index.html)!:the IV source buffer. The contents of the buffer are copied to protect against subsequent modification. | | Exceptions || |--------------------------------------|--------------------------------------| | `java.lang.IllegalArgumentException` | if`tLen`is negative, or`src`is null. | ### GCMParameterSpec Added in[API level 19](https://developer.android.com/guide/topics/manifest/uses-sdk-element.html#ApiLevels) ``` GCMParameterSpec(     tLen: Int,     src: ByteArray!,     offset: Int,     len: Int) ``` Constructs a GCMParameterSpec object using the specified authentication tag bit-length and a subset of the specified buffer as the IV. | Parameters || |----------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | `tLen` | [Int](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-int/index.html):the authentication tag length (in bits) | | `src` | [ByteArray](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-byte-array/index.html)!:the IV source buffer. The contents of the buffer are copied to protect against subsequent modification. | | `offset` | [Int](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-int/index.html):the offset in`src`where the IV starts | | `len` | [Int](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-int/index.html):the number of IV bytes | | Exceptions || |--------------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------| | `java.lang.IllegalArgumentException` | if`tLen`is negative,`src`is null,`len`or`offset`is negative, or the sum of`offset`and`len`is greater than the length of the`src`byte array. | ## Public methods ### getIV Added in[API level 19](https://developer.android.com/guide/topics/manifest/uses-sdk-element.html#ApiLevels) ``` open fun getIV(): ByteArray! ``` Returns the Initialization Vector (IV). | Return || |------------------------------------------------------------------------------------------|--------------------------------------------------------------| | [ByteArray](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-byte-array/index.html)! | the IV. Creates a new array each time this method is called. | ### getTLen Added in[API level 19](https://developer.android.com/guide/topics/manifest/uses-sdk-element.html#ApiLevels) ``` open fun getTLen(): Int ``` Returns the authentication tag length. | Return || |----------------------------------------------------------------------------|-----------------------------------------| | [Int](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-int/index.html) | the authentication tag length (in bits) |