AesGcmParams
AesGcmParams:
object
The AesGcmParams dictionary of the Web Crypto API represents the object that should be passed as the algorithm parameter into SubtleCrypto.encrypt, SubtleCrypto.decrypt, SubtleCrypto.wrapKey, or SubtleCrypto.unwrapKey, when using the AES-GCM algorithm. For details of how to supply appropriate values for this parameter, see the specification for AES-GCM: NIST SP800-38D, in particular section 5.2.1.1 on Input Data.
Type declaration
additionalData?
optionaladditionalData:BufferSource
An ArrayBuffer, a TypedArray, or a DataView. This contains additional data
that will not be encrypted but will be authenticated along with the encrypted data. If additionalData
is given here then the same data must be given in the corresponding call to SubtleCrypto.decrypt: if the data
given to the SubtleCrypto.decrypt call does not match the original data, the decryption will throw an exception.
This gives you a way to authenticate associated data without having to encrypt it.
The bit length of additionalData must be smaller than 2^64 - 1.
The additionalData property is optional and may be omitted without compromising the security of the encryption operation.
iv
iv:
BufferSource
An ArrayBuffer, a TypedArray, or a DataView with the initialization vector.
This must be unique for every encryption operation carried out with a given key. Put another way:
never reuse an IV with the same key. The AES-GCM specification recommends that the IV should be
96 bits long, and typically contains bits from a random number generator. Section 8.2 of the
specification outlines methods for constructing IVs. Note that the IV does not have to be secret,
just unique: so it is OK, for example, to transmit it in the clear alongside the encrypted message.
name
name:
string
A string. This should be set to AES-GCM.
tagLength?
optionaltagLength:number
A Number. This determines the size in bits of the authentication tag generated in the encryption operation and used for authentication in the corresponding decryption.
The Web Crypto API specification requires this to have one of the following values: 32, 64, 96, 104, 112, 120, or 128. On the other hand, the AES-GCM specification recommends that it should be 96, 104, 112, 120, or 128, although 32 or 64 bits may be acceptable in some applications. For additional guidance, see Appendix C of the NIST Publication on "Recommendation for Block Cipher Modes of Operation".
tagLength is optional and defaults to 128 if it is not specified.
Last updated: Sep 30, 2025
