diff --git a/packages/cre-sdk/src/sdk/utils/encryption.test.ts b/packages/cre-sdk/src/sdk/utils/encryption.test.ts
new file mode 100644
index 00000000..103f7c23
--- /dev/null
+++ b/packages/cre-sdk/src/sdk/utils/encryption.test.ts
@@ -0,0 +1,94 @@
+import { describe, expect, it } from 'bun:test'
+import {
+	ENCRYPTION_KEY_SECRET_NAME,
+	createRequestForEncryptedResponse,
+	decryptResponseBody,
+	deriveEncryptionKey,
+} from './encryption'
+
+// Cross-language test vector (must match Go output).
+const TEST_PASSPHRASE = 'test-passphrase-for-ci'
+const TEST_EXPECTED_HEX =
+	'521af99325c07c9bd0d224c5bf3ca25666c68b5fbb7fa7884019b4f60a8e6eb5'
+
+function toHex(bytes: Uint8Array): string {
+	return Array.from(bytes)
+		.map((b) => b.toString(16).padStart(2, '0'))
+		.join('')
+}
+
+describe('deriveEncryptionKey', () => {
+	it('produces deterministic output for the same passphrase', async () => {
+		const k1 = await deriveEncryptionKey('my-passphrase')
+		const k2 = await deriveEncryptionKey('my-passphrase')
+		expect(toHex(k1)).toBe(toHex(k2))
+	})
+
+	it('produces different output for different passphrases', async () => {
+		const k1 = await deriveEncryptionKey('passphrase-a')
+		const k2 = await deriveEncryptionKey('passphrase-b')
+		expect(toHex(k1)).not.toBe(toHex(k2))
+	})
+
+	it('matches the Go cross-language test vector', async () => {
+		const key = await deriveEncryptionKey(TEST_PASSPHRASE)
+		expect(toHex(key)).toBe(TEST_EXPECTED_HEX)
+	})
+})
+
+describe('createRequestForEncryptedResponse', () => {
+	it('sets encryptOutput and injects the secret identifier (JSON input)', () => {
+		const req = createRequestForEncryptedResponse(
+			{ url: 'https://example.com', method: 'GET' },
+			'0xDeaDBeeF',
+		)
+
+		expect(req.request?.encryptOutput).toBe(true)
+		expect(req.vaultDonSecrets).toHaveLength(1)
+		expect(req.vaultDonSecrets[0].key).toBe(ENCRYPTION_KEY_SECRET_NAME)
+		expect(req.vaultDonSecrets[0].owner).toBe('0xDeaDBeeF')
+	})
+})
+
+describe('decryptResponseBody', () => {
+	it('round-trips encrypt then decrypt', async () => {
+		const passphrase = 'round-trip-test'
+		const plaintext = new TextEncoder().encode('hello confidential http')
+
+		const keyBytes = await deriveEncryptionKey(passphrase)
+
+		// Encrypt using Web Crypto (simulates enclave behavior).
+		const key = await crypto.subtle.importKey('raw', keyBytes, 'AES-GCM', false, ['encrypt'])
+		const nonce = crypto.getRandomValues(new Uint8Array(12))
+		const ciphertextBuf = await crypto.subtle.encrypt(
+			{ name: 'AES-GCM', iv: nonce },
+			key,
+			plaintext,
+		)
+
+		// Wire format: [nonce][ciphertext+tag]
+		const wire = new Uint8Array(nonce.length + ciphertextBuf.byteLength)
+		wire.set(nonce, 0)
+		wire.set(new Uint8Array(ciphertextBuf), nonce.length)
+
+		const decrypted = await decryptResponseBody(wire, passphrase)
+		expect(new TextDecoder().decode(decrypted)).toBe('hello confidential http')
+	})
+
+	it('fails with wrong passphrase', async () => {
+		const keyBytes = await deriveEncryptionKey('correct-passphrase')
+		const key = await crypto.subtle.importKey('raw', keyBytes, 'AES-GCM', false, ['encrypt'])
+		const nonce = crypto.getRandomValues(new Uint8Array(12))
+		const ciphertextBuf = await crypto.subtle.encrypt(
+			{ name: 'AES-GCM', iv: nonce },
+			key,
+			new TextEncoder().encode('secret'),
+		)
+
+		const wire = new Uint8Array(nonce.length + ciphertextBuf.byteLength)
+		wire.set(nonce, 0)
+		wire.set(new Uint8Array(ciphertextBuf), nonce.length)
+
+		expect(decryptResponseBody(wire, 'wrong-passphrase')).rejects.toThrow()
+	})
+})
diff --git a/packages/cre-sdk/src/sdk/utils/encryption.ts b/packages/cre-sdk/src/sdk/utils/encryption.ts
new file mode 100644
index 00000000..156f1c28
--- /dev/null
+++ b/packages/cre-sdk/src/sdk/utils/encryption.ts
@@ -0,0 +1,101 @@
+import { create } from '@bufbuild/protobuf'
+import type {
+	ConfidentialHTTPRequest,
+	HTTPRequest,
+	HTTPRequestJson,
+} from '@cre/generated/capabilities/networking/confidentialhttp/v1alpha/client_pb'
+import {
+	ConfidentialHTTPRequestSchema,
+	HTTPRequestSchema,
+	SecretIdentifierSchema,
+} from '@cre/generated/capabilities/networking/confidentialhttp/v1alpha/client_pb'
+
+/** VaultDON secret name used for AES-GCM encryption of confidential HTTP responses. */
+export const ENCRYPTION_KEY_SECRET_NAME = 'san_marino_aes_gcm_encryption_key'
+
+/** HKDF info parameter shared across all language implementations. */
+const HKDF_INFO = 'confidential-http-encryption-key-v1'
+
+const AES_KEY_LEN = 32
+const GCM_NONCE_LEN = 12
+
+/**
+ * Derives a 32-byte AES-256 key from a passphrase using HKDF-SHA256.
+ *
+ * Parameters match the Go implementation:
+ * - Salt: empty
+ * - Info: "confidential-http-encryption-key-v1"
+ * - IKM: passphrase (UTF-8 bytes)
+ */
+export async function deriveEncryptionKey(passphrase: string): Promise<Uint8Array> {
+	const encoder = new TextEncoder()
+	const ikm = encoder.encode(passphrase)
+	const info = encoder.encode(HKDF_INFO)
+
+	// Import the passphrase as raw key material for HKDF.
+	const baseKey = await crypto.subtle.importKey('raw', ikm, 'HKDF', false, ['deriveBits'])
+
+	const bits = await crypto.subtle.deriveBits(
+		{
+			name: 'HKDF',
+			hash: 'SHA-256',
+			salt: new Uint8Array(0),
+			info,
+		},
+		baseKey,
+		AES_KEY_LEN * 8,
+	)
+
+	return new Uint8Array(bits)
+}
+
+/**
+ * Builds a ConfidentialHTTPRequest with encryptOutput=true and the AES key
+ * SecretIdentifier auto-injected.
+ *
+ * Accepts either a protobuf HTTPRequest message or a plain HTTPRequestJson object.
+ */
+export function createRequestForEncryptedResponse(
+	req: HTTPRequest | HTTPRequestJson,
+	owner: string,
+): ConfidentialHTTPRequest {
+	// If req is a plain JSON object (no $typeName), convert to protobuf message.
+	const httpReq = isHTTPRequestMessage(req) ? req : create(HTTPRequestSchema, req)
+	httpReq.encryptOutput = true
+
+	return create(ConfidentialHTTPRequestSchema, {
+		request: httpReq,
+		vaultDonSecrets: [
+			create(SecretIdentifierSchema, {
+				key: ENCRYPTION_KEY_SECRET_NAME,
+				owner,
+			}),
+		],
+	})
+}
+
+/**
+ * Decrypts an AES-GCM encrypted response body using the same passphrase that
+ * was used to store the encryption key.
+ *
+ * Wire format: [12-byte nonce][ciphertext+GCM tag]
+ */
+export async function decryptResponseBody(
+	ciphertext: Uint8Array,
+	passphrase: string,
+): Promise<Uint8Array> {
+	const keyBytes = await deriveEncryptionKey(passphrase)
+
+	const nonce = ciphertext.slice(0, GCM_NONCE_LEN)
+	const encrypted = ciphertext.slice(GCM_NONCE_LEN)
+
+	const key = await crypto.subtle.importKey('raw', keyBytes, 'AES-GCM', false, ['decrypt'])
+
+	const plaintext = await crypto.subtle.decrypt({ name: 'AES-GCM', iv: nonce }, key, encrypted)
+
+	return new Uint8Array(plaintext)
+}
+
+function isHTTPRequestMessage(req: HTTPRequest | HTTPRequestJson): req is HTTPRequest {
+	return '$typeName' in req
+}
diff --git a/packages/cre-sdk/src/sdk/utils/index.ts b/packages/cre-sdk/src/sdk/utils/index.ts
index 9272593f..4f984d7b 100644
--- a/packages/cre-sdk/src/sdk/utils/index.ts
+++ b/packages/cre-sdk/src/sdk/utils/index.ts
@@ -7,3 +7,4 @@ export * from './safe-json-stringify'
 export * from './values/consensus_aggregators'
 export * from './values/serializer_types'
 export * from './values/value'
+export * from './encryption'