diff --git a/yarn-project/aztec-rpc/src/aztec_rpc_server/note_preimage/index.ts b/yarn-project/aztec-rpc/src/aztec_rpc_server/note_preimage/index.ts
deleted file mode 100644
index 9f87e68e478..00000000000
--- a/yarn-project/aztec-rpc/src/aztec_rpc_server/note_preimage/index.ts
+++ /dev/null
@@ -1,2 +0,0 @@
-export * from './note_preimage.js';
-export * from './encrypt_note_preimage.js';
diff --git a/yarn-project/aztec-rpc/src/aztec_rpc_server/note_preimage/note_preimage.test.ts b/yarn-project/aztec-rpc/src/aztec_rpc_server/note_preimage/note_preimage.test.ts
deleted file mode 100644
index 8aafb8dc855..00000000000
--- a/yarn-project/aztec-rpc/src/aztec_rpc_server/note_preimage/note_preimage.test.ts
+++ /dev/null
@@ -1,28 +0,0 @@
-import { Grumpkin } from '@aztec/barretenberg.js/crypto';
-import { BarretenbergWasm } from '@aztec/barretenberg.js/wasm';
-import { AztecAddress } from '@aztec/foundation/aztec-address';
-import { randomBytes } from '@aztec/foundation/crypto';
-import { Fr } from '@aztec/foundation/fields';
-import { NotePreImage } from './note_preimage.js';
-
-describe('note_preimage', () => {
-  it('convert to and from buffer', () => {
-    const fields = Array.from({ length: 5 }).map(() => Fr.random());
-    const notePreImage = new NotePreImage(fields);
-    const buf = notePreImage.toBuffer();
-    expect(NotePreImage.fromBuffer(buf)).toEqual(notePreImage);
-  });
-
-  it('convert to and from encrypted buffer', async () => {
-    const grumpkin = new Grumpkin(await BarretenbergWasm.new());
-    const fields = Array.from({ length: 5 }).map(() => Fr.random());
-    const notePreImage = new NotePreImage(fields);
-    const ownerPrivKey = randomBytes(32);
-    const ownerPubKey = AztecAddress.fromBuffer(grumpkin.mul(Grumpkin.generator, ownerPrivKey));
-    const ephPrivKey = randomBytes(32);
-    const encrypted = notePreImage.toEncryptedBuffer(ownerPubKey, ephPrivKey, grumpkin);
-    const decrypted = NotePreImage.fromEncryptedBuffer(encrypted, ownerPrivKey, grumpkin);
-    expect(decrypted).not.toBeUndefined();
-    expect(decrypted).toEqual(notePreImage);
-  });
-});
diff --git a/yarn-project/aztec-rpc/src/aztec_rpc_server/note_preimage/note_preimage.ts b/yarn-project/aztec-rpc/src/aztec_rpc_server/note_preimage/note_preimage.ts
deleted file mode 100644
index 29e4f43db2b..00000000000
--- a/yarn-project/aztec-rpc/src/aztec_rpc_server/note_preimage/note_preimage.ts
+++ /dev/null
@@ -1,31 +0,0 @@
-import { BufferReader, serializeBufferArrayToVector } from '@aztec/foundation';
-import { decryptNotePreimage, encryptNotePreimage } from './encrypt_note_preimage.js';
-import { Grumpkin } from '@aztec/barretenberg.js/crypto';
-import { Fr } from '@aztec/foundation/fields';
-import { AztecAddress } from '@aztec/foundation/aztec-address';
-
-export class NotePreImage {
-  constructor(public readonly fields: Fr[]) {}
-
-  static fromBuffer(buf: Buffer | BufferReader) {
-    const reader = BufferReader.asReader(buf);
-    const fields = reader.readVector(Fr);
-    return new NotePreImage(fields);
-  }
-
-  public toBuffer() {
-    return serializeBufferArrayToVector(this.fields.map(f => f.toBuffer()));
-  }
-
-  public toEncryptedBuffer(ownerPubKey: AztecAddress, ephPrivKey: Buffer, grumpkin: Grumpkin) {
-    return encryptNotePreimage(this, ownerPubKey, ephPrivKey, grumpkin);
-  }
-
-  static fromEncryptedBuffer(data: Buffer, ownerPrivKey: Buffer, grumpkin: Grumpkin) {
-    const buf = decryptNotePreimage(data, ownerPrivKey, grumpkin);
-    if (!buf) {
-      return;
-    }
-    return NotePreImage.fromBuffer(buf);
-  }
-}
diff --git a/yarn-project/aztec-rpc/src/aztec_rpc_server/note_preimage/browserify-cipher.d.ts b/yarn-project/aztec-rpc/src/aztec_rpc_server/tx_aux_data/browserify-cipher.d.ts
similarity index 100%
rename from yarn-project/aztec-rpc/src/aztec_rpc_server/note_preimage/browserify-cipher.d.ts
rename to yarn-project/aztec-rpc/src/aztec_rpc_server/tx_aux_data/browserify-cipher.d.ts
diff --git a/yarn-project/aztec-rpc/src/aztec_rpc_server/tx_aux_data/encrypt_buffer.test.ts b/yarn-project/aztec-rpc/src/aztec_rpc_server/tx_aux_data/encrypt_buffer.test.ts
new file mode 100644
index 00000000000..d94c4a3b5f9
--- /dev/null
+++ b/yarn-project/aztec-rpc/src/aztec_rpc_server/tx_aux_data/encrypt_buffer.test.ts
@@ -0,0 +1,34 @@
+import { Grumpkin } from '@aztec/barretenberg.js/crypto';
+import { BarretenbergWasm } from '@aztec/barretenberg.js/wasm';
+import { AztecAddress } from '@aztec/foundation/aztec-address';
+import { randomBytes } from '@aztec/foundation/crypto';
+import { decryptBuffer, encryptBuffer } from './encrypt_buffer.js';
+
+describe('encrypt buffer', () => {
+  it('convert to and from encrypted buffer', async () => {
+    const grumpkin = new Grumpkin(await BarretenbergWasm.new());
+    const data = randomBytes(253);
+    const ownerPrivKey = randomBytes(32);
+    const ownerPubKey = AztecAddress.fromBuffer(grumpkin.mul(Grumpkin.generator, ownerPrivKey));
+    const ephPrivKey = randomBytes(32);
+    const encrypted = encryptBuffer(data, ownerPubKey, ephPrivKey, grumpkin);
+    const decrypted = decryptBuffer(encrypted, ownerPrivKey, grumpkin);
+    expect(decrypted).not.toBeUndefined();
+    expect(decrypted).toEqual(data);
+  });
+
+  it('decrypting gibberish returns undefined', async () => {
+    const grumpkin = new Grumpkin(await BarretenbergWasm.new());
+    const data = randomBytes(253);
+    const ownerPrivKey = randomBytes(32);
+    const ephPrivKey = randomBytes(32);
+    const ownerPubKey = AztecAddress.fromBuffer(grumpkin.mul(Grumpkin.generator, ownerPrivKey));
+    const encrypted = encryptBuffer(data, ownerPubKey, ephPrivKey, grumpkin);
+
+    // Introduce gibberish.
+    const gibberish = Buffer.concat([randomBytes(8), encrypted.subarray(8)]);
+
+    const decrypted = decryptBuffer(gibberish, ownerPrivKey, grumpkin);
+    expect(decrypted).toBeUndefined();
+  });
+});
diff --git a/yarn-project/aztec-rpc/src/aztec_rpc_server/note_preimage/encrypt_note_preimage.ts b/yarn-project/aztec-rpc/src/aztec_rpc_server/tx_aux_data/encrypt_buffer.ts
similarity index 64%
rename from yarn-project/aztec-rpc/src/aztec_rpc_server/note_preimage/encrypt_note_preimage.ts
rename to yarn-project/aztec-rpc/src/aztec_rpc_server/tx_aux_data/encrypt_buffer.ts
index cb7d2bc589a..11f59bf7461 100644
--- a/yarn-project/aztec-rpc/src/aztec_rpc_server/note_preimage/encrypt_note_preimage.ts
+++ b/yarn-project/aztec-rpc/src/aztec_rpc_server/tx_aux_data/encrypt_buffer.ts
@@ -1,7 +1,6 @@
 import { createCipheriv, createDecipheriv } from 'browserify-cipher';
 import { Grumpkin } from '@aztec/barretenberg.js/crypto';
 import { numToUInt8 } from '@aztec/foundation/serialize';
-import { NotePreImage } from './note_preimage.js';
 import { sha256 } from '@aztec/foundation/crypto';
 import { AztecAddress } from '@aztec/foundation/aztec-address';
 
@@ -12,29 +11,17 @@ function deriveAESSecret(ecdhPubKey: AztecAddress, ecdhPrivKey: Buffer, grumpkin
   return hash;
 }
 
-/**
- * Returns the AES encrypted "viewing key".
- * [AES: [32 bytes value][4 bytes assetId][4 bytes accountRequired][32 bytes creatorPubKey]] [64 bytes ephPubKey]
- * @param data = { value, assetId, accountRequired, creatorPubKey };
- * @param ownerPubKey - the public key contained within a value note
- * @param ephPrivKey - a random field element (also used alongside the ownerPubKey in deriving a value note's secret)
- */
-export function encryptNotePreimage(
-  data: NotePreImage,
-  ownerPubKey: AztecAddress,
-  ephPrivKey: Buffer,
-  grumpkin: Grumpkin,
-) {
+export function encryptBuffer(data: Buffer, ownerPubKey: AztecAddress, ephPrivKey: Buffer, grumpkin: Grumpkin) {
   const ephPubKey = grumpkin.mul(Grumpkin.generator, ephPrivKey);
   const aesSecret = deriveAESSecret(ownerPubKey, ephPrivKey, grumpkin);
   const aesKey = aesSecret.subarray(0, 16);
   const iv = aesSecret.subarray(16, 32);
   const cipher = createCipheriv('aes-128-cbc', aesKey, iv);
-  const plaintext = Buffer.concat([iv.subarray(0, 8), data.toBuffer()]);
+  const plaintext = Buffer.concat([iv.subarray(0, 8), data]);
   return Buffer.concat([cipher.update(plaintext), cipher.final(), ephPubKey]);
 }
 
-export function decryptNotePreimage(data: Buffer, ownerPrivKey: Buffer, grumpkin: Grumpkin) {
+export function decryptBuffer(data: Buffer, ownerPrivKey: Buffer, grumpkin: Grumpkin) {
   const ephPubKey = new AztecAddress(data.subarray(-64));
   const aesSecret = deriveAESSecret(ephPubKey, ownerPrivKey, grumpkin);
   const aesKey = aesSecret.subarray(0, 16);
diff --git a/yarn-project/aztec-rpc/src/aztec_rpc_server/tx_aux_data/index.ts b/yarn-project/aztec-rpc/src/aztec_rpc_server/tx_aux_data/index.ts
new file mode 100644
index 00000000000..397972f4947
--- /dev/null
+++ b/yarn-project/aztec-rpc/src/aztec_rpc_server/tx_aux_data/index.ts
@@ -0,0 +1,2 @@
+export * from './note_preimage.js';
+export * from './encrypt_buffer.js';
diff --git a/yarn-project/aztec-rpc/src/aztec_rpc_server/tx_aux_data/note_preimage.test.ts b/yarn-project/aztec-rpc/src/aztec_rpc_server/tx_aux_data/note_preimage.test.ts
new file mode 100644
index 00000000000..e27a3fa4c54
--- /dev/null
+++ b/yarn-project/aztec-rpc/src/aztec_rpc_server/tx_aux_data/note_preimage.test.ts
@@ -0,0 +1,11 @@
+import { Fr } from '@aztec/foundation/fields';
+import { NotePreimage } from './note_preimage.js';
+
+describe('note_preimage', () => {
+  it('convert to and from buffer', () => {
+    const fields = Array.from({ length: 5 }).map(() => Fr.random());
+    const notePreImage = new NotePreimage(fields);
+    const buf = notePreImage.toBuffer();
+    expect(NotePreimage.fromBuffer(buf)).toEqual(notePreImage);
+  });
+});
diff --git a/yarn-project/aztec-rpc/src/aztec_rpc_server/tx_aux_data/note_preimage.ts b/yarn-project/aztec-rpc/src/aztec_rpc_server/tx_aux_data/note_preimage.ts
new file mode 100644
index 00000000000..39c6a7a97c1
--- /dev/null
+++ b/yarn-project/aztec-rpc/src/aztec_rpc_server/tx_aux_data/note_preimage.ts
@@ -0,0 +1,10 @@
+import { Fr } from '@aztec/foundation/fields';
+import { Vector } from '@aztec/circuits.js';
+import { BufferReader } from '@aztec/foundation/serialize';
+
+export class NotePreimage extends Vector<Fr> {
+  static fromBuffer(buffer: Buffer | BufferReader) {
+    const reader = BufferReader.asReader(buffer);
+    return new NotePreimage(reader.readVector(Fr));
+  }
+}
diff --git a/yarn-project/aztec-rpc/src/aztec_rpc_server/tx_aux_data/tx_aux_data.test.ts b/yarn-project/aztec-rpc/src/aztec_rpc_server/tx_aux_data/tx_aux_data.test.ts
new file mode 100644
index 00000000000..b8d2f538f09
--- /dev/null
+++ b/yarn-project/aztec-rpc/src/aztec_rpc_server/tx_aux_data/tx_aux_data.test.ts
@@ -0,0 +1,34 @@
+import { Grumpkin } from '@aztec/barretenberg.js/crypto';
+import { BarretenbergWasm } from '@aztec/barretenberg.js/wasm';
+import { AztecAddress, randomBytes } from '@aztec/foundation';
+import { Fr } from '@aztec/foundation/fields';
+import { NotePreimage } from './note_preimage.js';
+import { TxAuxData } from './tx_aux_data.js';
+
+const randomTxAuxData = () => {
+  const fields = Array.from({ length: 5 }).map(() => Fr.random());
+  const notePreImage = new NotePreimage(fields);
+  const contractAddress = AztecAddress.random();
+  const storageSlot = Fr.random();
+  return new TxAuxData(notePreImage, contractAddress, storageSlot);
+};
+
+describe('tx_aux_data', () => {
+  it('convert to and from buffer', () => {
+    const txAuxData = randomTxAuxData();
+    const buf = txAuxData.toBuffer();
+    expect(TxAuxData.fromBuffer(buf)).toEqual(txAuxData);
+  });
+
+  it('convert to and from encrypted buffer', async () => {
+    const grumpkin = new Grumpkin(await BarretenbergWasm.new());
+    const txAuxData = randomTxAuxData();
+    const ownerPrivKey = randomBytes(32);
+    const ownerPubKey = AztecAddress.fromBuffer(grumpkin.mul(Grumpkin.generator, ownerPrivKey));
+    const ephPrivKey = randomBytes(32);
+    const encrypted = txAuxData.toEncryptedBuffer(ownerPubKey, ephPrivKey, grumpkin);
+    const decrypted = TxAuxData.fromEncryptedBuffer(encrypted, ownerPrivKey, grumpkin);
+    expect(decrypted).not.toBeUndefined();
+    expect(decrypted).toEqual(txAuxData);
+  });
+});
diff --git a/yarn-project/aztec-rpc/src/aztec_rpc_server/tx_aux_data/tx_aux_data.ts b/yarn-project/aztec-rpc/src/aztec_rpc_server/tx_aux_data/tx_aux_data.ts
new file mode 100644
index 00000000000..196c0790b20
--- /dev/null
+++ b/yarn-project/aztec-rpc/src/aztec_rpc_server/tx_aux_data/tx_aux_data.ts
@@ -0,0 +1,32 @@
+import { Fr } from '@aztec/foundation/fields';
+import { AztecAddress } from '@aztec/circuits.js';
+import { BufferReader } from '@aztec/foundation/serialize';
+import { NotePreimage } from './note_preimage.js';
+import { serializeToBuffer } from '@aztec/circuits.js/utils';
+import { decryptBuffer, encryptBuffer } from './encrypt_buffer.js';
+import { Grumpkin } from '@aztec/barretenberg.js/crypto';
+
+export class TxAuxData {
+  constructor(public notePreImage: NotePreimage, public contractAddress: AztecAddress, public storageSlot: Fr) {}
+
+  static fromBuffer(buffer: Buffer | BufferReader) {
+    const reader = BufferReader.asReader(buffer);
+    return new TxAuxData(reader.readObject(NotePreimage), reader.readObject(AztecAddress), reader.readFr());
+  }
+
+  toBuffer() {
+    return serializeToBuffer([this.notePreImage, this.contractAddress, this.storageSlot]);
+  }
+
+  public toEncryptedBuffer(ownerPubKey: AztecAddress, ephPrivKey: Buffer, grumpkin: Grumpkin) {
+    return encryptBuffer(this.toBuffer(), ownerPubKey, ephPrivKey, grumpkin);
+  }
+
+  static fromEncryptedBuffer(data: Buffer, ownerPrivKey: Buffer, grumpkin: Grumpkin) {
+    const buf = decryptBuffer(data, ownerPrivKey, grumpkin);
+    if (!buf) {
+      return;
+    }
+    return TxAuxData.fromBuffer(buf);
+  }
+}
diff --git a/yarn-project/aztec-rpc/src/database/note_dao.ts b/yarn-project/aztec-rpc/src/database/note_dao.ts
index 244b9771cb0..d2d3361e47c 100644
--- a/yarn-project/aztec-rpc/src/database/note_dao.ts
+++ b/yarn-project/aztec-rpc/src/database/note_dao.ts
@@ -1,11 +1,11 @@
 import { AztecAddress, Fr } from '@aztec/circuits.js';
-import { NotePreImage } from '../aztec_rpc_server/note_preimage/note_preimage.js';
+import { NotePreimage } from '../aztec_rpc_server/tx_aux_data/note_preimage.js';
 
 export interface NoteDao {
   // Properties from the encrypted note
   contractAddress: AztecAddress;
   contractSlot: Fr;
-  notePreimage: NotePreImage;
+  notePreimage: NotePreimage;
   // Computed properties
   nullifier: Fr;
   // The location in the tree
diff --git a/yarn-project/aztec-rpc/src/simulator_oracle/index.ts b/yarn-project/aztec-rpc/src/simulator_oracle/index.ts
index f81cd582461..cdcf072b862 100644
--- a/yarn-project/aztec-rpc/src/simulator_oracle/index.ts
+++ b/yarn-project/aztec-rpc/src/simulator_oracle/index.ts
@@ -13,7 +13,7 @@ export class SimulatorOracle implements DBOracle {
   async getNotes(contractAddress: AztecAddress, storageSlot: Fr): Promise<NoteLoadOracleInputs[]> {
     const noteDaos = await this.db.getNotes(contractAddress, storageSlot);
     return noteDaos.map(noteDao => ({
-      note: noteDao.notePreimage.fields,
+      note: noteDao.notePreimage.items,
       siblingPath: [], // TODO get this from node
       index: noteDao.index,
     }));
diff --git a/yarn-project/foundation/src/aztec-address/index.ts b/yarn-project/foundation/src/aztec-address/index.ts
index 8c575146260..fb0db5746dc 100644
--- a/yarn-project/foundation/src/aztec-address/index.ts
+++ b/yarn-project/foundation/src/aztec-address/index.ts
@@ -13,7 +13,7 @@ export class AztecAddress {
 
   static fromBuffer(bufferOrReader: Buffer | BufferReader) {
     const reader = BufferReader.asReader(bufferOrReader);
-    return new AztecAddress(reader.readBytes(AztecAddress.SIZE_IN_BYTES));
+    return new AztecAddress(reader.readBytes(this.SIZE_IN_BYTES));
   }
 
   public static fromString(address: string) {
@@ -21,7 +21,7 @@ export class AztecAddress {
   }
 
   public static random() {
-    return new AztecAddress(randomBytes(AztecAddress.SIZE_IN_BYTES));
+    return new AztecAddress(randomBytes(this.SIZE_IN_BYTES));
   }
 
   public equals(rhs: AztecAddress) {