# Login Flow

MIB uses a two-phase authentication model:

| Phase | Trigger | Key used |
|---|---|---|
| **Device Registration** | First time this device+account pair is seen | `DEFAULT_KEY` → DH session key |
| **Regular Login** | Every subsequent login (stored `key1`/`key2`) | `key1` → DH session key |

---

## Password Hashing (`pgf03`)

The password is never sent in plaintext. Required by both `C41` (registration) and `A41` (login).

```
pgf03 = SHA256( clientSalt + SHA256( userSalt + SHA256( password ) ) )
```

All SHA-256 values are uppercase hex strings. `clientSalt` is a fresh random 32-character alphanumeric string each time.

```python
import hashlib

def compute_pgf03(password: str, user_salt: str, client_salt: str) -> str:
    h1 = hashlib.sha256(password.encode()).hexdigest().upper()
    h2 = hashlib.sha256((user_salt + h1).encode()).hexdigest().upper()
    return hashlib.sha256((client_salt + h2).encode()).hexdigest().upper()
```

---

## Device Registration Flow (first time only)

```
[0] sfunc=r  DEFAULT_KEY  →  DH exchange  →  derive session_key_1, get xxid + nonceGenerator
[1] sfunc=n  A44          →  get userSalt
[2] sfunc=n  C41          →  submit credentials  →  returns key1, key2 (persist!)
[3] sfunc=n  C42          →  verify OTP
[4–8] regular login (below) using the key1/key2 just received
```

---

## Regular Login Flow

```
[0] sfunc=i  key1         →  DH exchange  →  derive session_key_2, get xxid + nonceGenerator
[1] sfunc=n  A44          →  get userSalt
[2] sfunc=n  A41          →  submit credentials  →  returns otpTypes, email, uuid
[3] sfunc=n  P41          →  fetch profile image (optional)
[4] sfunc=n  A42          →  verify OTP  →  session established
[5] sfunc=n  P47          →  select profile  →  returns accountBalance array
```

---

## Step-by-Step Reference

### [0] Initial Key Exchange — `sfunc=r`

**Key**: `DEFAULT_KEY = 8M3L9SBF1AC4FRE56788M3L9SBF1AC4FRE5678`

**Request** (outer + inner are encrypted together):
```json
{
  "sfunc": "r",
  "data": {
    "cmod": "<G^A mod P as decimal string>",
    "appId": "IOS17.2-<15 random alphanumeric chars>",
    "routePath": "S40",
    "sodium": "<random 20-bit int as string>",
    "xxid": "<random 40-bit int as string>"
  }
}
```

**Response** (decrypted with `DEFAULT_KEY`):
```json
{
  "success": true,
  "reasonCode": "201",
  "reasonText": "Key generated successfully.",
  "smod": "<server DH public key as decimal string>",
  "nonceGenerator": "<instruction string>",
  "xxid": "<session token — use for all subsequent calls>",
  "sodium": "<server random>",
  "encMethod": 2
}
```

After: `session_key = derive_session_key(int(smod))`. Save `xxid` and `nonceGenerator`.

---

### [1] Get Auth Type — `sfunc=n`, `routePath: A44`

**Key**: session key

**Request**:
```json
{
  "sfunc": "n",
  "xxid": "<session xxid>",
  "data": {
    "uname": "<username>",
    "nonce": "<computed nonce>",
    "appId": "<appId>",
    "sodium": "<random>",
    "routePath": "A44",
    "xxid": "<session xxid>"
  }
}
```

**Response**:
```json
{
  "success": true,
  "data": [{ "loginType": "1", "userSalt": "<server salt>" }]
}
```

Use `userSalt` in `pgf03` computation.

---

### [2a] Device Registration Init — `sfunc=n`, `routePath: C41`

_First-time only._

**Request**:
```json
{
  "sfunc": "n",
  "xxid": "<session xxid>",
  "data": {
    "uname": "<username>",
    "pgf03": "<computed>",
    "clientSalt": "<random 32-char string>",
    "nonce": "<nonce>",
    "appId": "<appId>",
    "sodium": "<random>",
    "routePath": "C41",
    "xxid": "<session xxid>"
  }
}
```

**Response**:
```json
{
  "success": true,
  "reasonCode": "201",
  "primaryOTPType": "3",
  "otpTypes": [2, 3],
  "fullName": "<user full name>",
  "customerImgHash": "<hash>"
}
```

---

### [3a] OTP Verification (Registration) — `sfunc=n`, `routePath: C42`

_First-time only. Receive and persist `key1`/`key2`._

**Request**:
```json
{
  "sfunc": "n",
  "xxid": "<session xxid>",
  "data": {
    "otp": "<6-digit OTP>",
    "uname": "<username>",
    "otpType": "3",
    "nonce": "<nonce>",
    "appId": "<appId>",
    "sodium": "<random>",
    "routePath": "C42",
    "xxid": "<session xxid>"
  }
}
```

**Response**:
```json
{
  "success": true,
  "reasonCode": "101",
  "data": [{
    "key1": "<store securely — Blowfish key for next sfunc=i>",
    "key2": "<store securely — sent plaintext in sfunc=i wrapper>",
    "appId": "<appId>",
    "encryptionMethod": "2"
  }]
}
```

`key1` and `key2` are long-lived device credentials. Store them securely on the device.

---

### [0b] Authenticated Key Exchange — `sfunc=i`

_Regular login. `key2` is a separate unencrypted outer field._

**Key**: `key1`

Form body: `key2=<key2>&sfunc=i&data=<encrypted payload>`

**Encrypted payload**:
```json
{
  "sfunc": "i",
  "key2": "<key2>",
  "data": {
    "cmod": "<G^A mod P>",
    "appId": "<appId>",
    "routePath": "S40",
    "sodium": "<random 20-bit int>",
    "xxid": "<random 40-bit int>"
  }
}
```

**Response** (decrypted with `key1`):
```json
{
  "success": true,
  "smod": "<new server DH public key>",
  "nonceGenerator": "<new instruction string>",
  "xxid": "<new session token>",
  "encMethod": 2
}
```

After: derive new session key, replace `xxid` and `nonceGenerator`.

---

### [2b] Regular Login Init — `sfunc=n`, `routePath: A41`

**Key**: session key

**Request**:
```json
{
  "sfunc": "n",
  "xxid": "<session xxid>",
  "data": {
    "uname": "<username>",
    "pgf03": "<computed>",
    "clientSalt": "<random 32-char>",
    "pmodTime": 0,
    "requireBankData": 1,
    "nonce": "<nonce>",
    "appId": "<appId>",
    "sodium": "<random>",
    "routePath": "A41",
    "xxid": "<session xxid>"
  }
}
```

**Response**:
```json
{
  "success": true,
  "reasonCode": "104",
  "primaryOTPType": "3",
  "otpTypes": [2, 3],
  "email": "<masked email>",
  "uuid": "<uuid1>",
  "uuid2": "<uuid2>"
}
```

---

### [3b] Get Profile Image — `sfunc=n`, `routePath: P41`

Optional. Fetch the user's avatar to display on the OTP screen.

**Request**:
```json
{
  "sfunc": "n",
  "xxid": "<session xxid>",
  "data": {
    "imageHash": "<customerImgHash from C41/A41>",
    "nonce": "<nonce>",
    "appId": "<appId>",
    "sodium": "<random>",
    "routePath": "P41",
    "xxid": "<session xxid>"
  }
}
```

**Response**:
```json
{
  "success": true,
  "reasonCode": "201",
  "profileImage": "<base64-encoded JPEG>"
}
```

---

### [4b] OTP Verification (Login) — `sfunc=n`, `routePath: A42`

**Request**:
```json
{
  "sfunc": "n",
  "xxid": "<session xxid>",
  "data": {
    "otp": "<6-digit OTP>",
    "uname": "<username>",
    "otpType": "3",
    "nonce": "<nonce>",
    "appId": "<appId>",
    "sodium": "<random>",
    "routePath": "A42",
    "xxid": "<session xxid>"
  }
}
```

After successful `A42`, the `xxid` and `nonceGenerator` from the `sfunc=i` response become the WebView session cookies. See [README](README.md) for the cookie format.

---

### [5] Select Profile — `sfunc=n`, `routePath: P47`

See [03-accounts.md](03-accounts.md) for the full P47 reference.

---

&nbsp;

---

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