Authenticate and decrypt AES-256-GCM ciphertext using IV
Authenticate and decrypt AES-256-GCM ciphertext using IV, authentication tag, and raw key or passphrase/salt
Request
- x-api-key: <your-api-key>
- Content-Type: application/json
Response
{
"algorithm": "<algorithm>",
"authenticated": true,
"plaintext": "<plaintext>",
"status": "success",
"tokensDeducted": 1
}What it does
Authenticate and decrypt AES-256-GCM ciphertext using IV, authentication tag, and raw key or passphrase/salt
Request
Body
| Field | Type | Required | Description |
|---|---|---|---|
associatedData | string | no | Optional Additional Authenticated Data (AAD) bound during encryption. |
ciphertext | string | yes | Ciphertext string encoded in specified inputEncoding. |
inputEncoding | enum | no | Encoding format of ciphertext, IV, tag, and salt parameters. One of: hex, base64, base64url. |
iv | string | yes | Initialization Vector (IV) generated during encryption. |
key | string | no | 32-byte key formatted in hex, base64, or raw string. |
keyEncoding | enum | no | One of: hex, base64, utf8. |
passphrase | string | no | Passphrase used to derive the 256-bit key via scrypt (requires salt). |
salt | string | no | Salt string generated during key derivation at encryption time (required if passphrase is used). |
tag | string | yes | 128-bit authentication tag generated during GCM encryption. |
Example request
{
"associatedData": "<associated data>",
"ciphertext": "<ciphertext>",
"inputEncoding": "hex",
"iv": "<iv>",
"key": "example",
"keyEncoding": "hex",
"passphrase": "<passphrase>",
"salt": "<salt>",
"tag": "<tag>"
}Response
| Field | Type | Description |
|---|---|---|
algorithm | string | |
authenticated | boolean | |
plaintext | string | |
status | string | |
tokensDeducted | integer |
Example response
{
"algorithm": "<algorithm>",
"authenticated": true,
"plaintext": "<plaintext>",
"status": "success",
"tokensDeducted": 1
}Errors
Every error answers with the same envelope: an HTTP status, a machine code and a sentence.
400 | The body or a parameter failed validation. The details array names the field. |
401 | No key, a revoked key or a wrong header. Send x-api-key. |
402 | The wallet cannot cover this call. Top up or wait for the monthly grant. |
404 | The resource does not exist, or it is not yours. Both answer identically and cost nothing. |
429 | Over the per-minute quota of your tier. Back off and retry. |
5xx | Upstream refused or timed out. The call is not billed. |
Code
curl -X POST 'https://app.castomapi.com/v1/crypto/decrypt' \
-H 'x-api-key: <your-api-key>' \
-H 'Content-Type: application/json' \
-d '{"associatedData": "<associated data>", "ciphertext": "<ciphertext>", "inputEncoding": "hex", "iv": "<iv>", "key": "example", "keyEncoding": "hex", "passphrase": "<passphrase>", "salt": "<salt>", "tag": "<tag>"}'const res = await fetch('https://app.castomapi.com/v1/crypto/decrypt', {
method: 'POST',
headers: { 'x-api-key': '<your-api-key>', 'Content-Type': 'application/json' },
body: JSON.stringify({"associatedData": "<associated data>", "ciphertext": "<ciphertext>", "inputEncoding": "hex", "iv": "<iv>", "key": "example", "keyEncoding": "hex", "passphrase": "<passphrase>", "salt": "<salt>", "tag": "<tag>"})
});
const data = await res.json();
console.log(data);import { request } from 'node:https';
// Node 18+ has fetch built in
const res = await fetch('https://app.castomapi.com/v1/crypto/decrypt', {
method: 'POST',
headers: { 'x-api-key': '<your-api-key>', 'Content-Type': 'application/json' },
body: JSON.stringify({"associatedData": "<associated data>", "ciphertext": "<ciphertext>", "inputEncoding": "hex", "iv": "<iv>", "key": "example", "keyEncoding": "hex", "passphrase": "<passphrase>", "salt": "<salt>", "tag": "<tag>"})
});
const data = await res.json();
console.log(data);import requests
res = requests.post(
'https://app.castomapi.com/v1/crypto/decrypt',
headers={'x-api-key': '<your-api-key>'},
json={"associatedData": "<associated data>", "ciphertext": "<ciphertext>", "inputEncoding": "hex", "iv": "<iv>", "key": "example", "keyEncoding": "hex", "passphrase": "<passphrase>", "salt": "<salt>", "tag": "<tag>"},
timeout=30,
)
print(res.json())<?php
$ch = curl_init('https://app.castomapi.com/v1/crypto/decrypt');
curl_setopt_array($ch, [
CURLOPT_CUSTOMREQUEST => 'POST',
CURLOPT_RETURNTRANSFER => true,
CURLOPT_HTTPHEADER => ['x-api-key: <your-api-key>', 'Content-Type: application/json'],
CURLOPT_POSTFIELDS => json_encode(['associatedData' => '<associated data>', 'ciphertext' => '<ciphertext>', 'inputEncoding' => 'hex', 'iv' => '<iv>', 'key' => 'example', 'keyEncoding' => 'hex', 'passphrase' => '<passphrase>', 'salt' => '<salt>', 'tag' => '<tag>']),
]);
$data = json_decode(curl_exec($ch), true);
print_r($data);Cost and limits
This operation needs no API key and costs nothing: called without a key it answers 200 and deducts zero tokens, up to 10 requests a minute per IP address.
Rate limits per minute
| No key | 10 |
| Free | 60 |
| Pro | 300 |
| Enterprise | 1200 |
Questions
What does Authenticate and decrypt AES-256-GCM ciphertext using IV cost?
This operation needs no API key and costs nothing: called without a key it answers 200 and deducts zero tokens, up to 10 requests a minute per IP address.
How do I authenticate?
Send your key in the x-api-key header. One key covers every metered endpoint; there is nothing to enable per endpoint.
Can I send an Authorization: Bearer token instead?
Not for a metered endpoint — those take the x-api-key header and nothing else. Bearer tokens belong to the account side: the dashboard and account APIs accept a JWT session, and castomapi-auth issues those through a standard OAuth2 handshake, with authorization code, client credentials and refresh grants. The auth service page covers it.
What are the limits?
10 requests a minute per IP with no key at all, 60 a minute on the free tier, 300 on Pro, 1200 on Enterprise. Above the no-key tier the quota is per account, across every endpoint.
OpenAPI: https://app.castomapi.com/docs/json