diff --git a/backend/app/core/dependencies.py b/backend/app/core/dependencies.py
new file mode 100644
index 0000000..900b5c0
--- /dev/null
+++ b/backend/app/core/dependencies.py
@@ -0,0 +1,55 @@
+"""FastAPI dependency functions for authentication and authorisation."""
+
+from fastapi import Depends, HTTPException, status
+from fastapi.security import HTTPBearer, HTTPAuthorizationCredentials
+from jose import JWTError
+from sqlalchemy.orm import Session
+
+from app.core.security import decode_access_token
+from app.database import get_db
+from app.models.user import User
+
+security = HTTPBearer()
+
+
+def get_current_user(
+    credentials: HTTPAuthorizationCredentials = Depends(security),
+    db: Session = Depends(get_db),
+) -> User:
+    """Extract and validate the JWT bearer token, then return the active user.
+
+    Raises 401 if the token is invalid/expired or the user is inactive.
+    """
+    try:
+        payload = decode_access_token(credentials.credentials)
+        user_id = int(payload["sub"])
+    except (JWTError, KeyError, ValueError):
+        raise HTTPException(
+            status_code=status.HTTP_401_UNAUTHORIZED,
+            detail="Invalid token",
+        )
+
+    user = (
+        db.query(User)
+        .filter(User.id == user_id, User.is_active == True)  # noqa: E712
+        .first()
+    )
+    if not user:
+        raise HTTPException(
+            status_code=status.HTTP_401_UNAUTHORIZED,
+            detail="User not found or inactive",
+        )
+    return user
+
+
+def require_admin(user: User = Depends(get_current_user)) -> User:
+    """Require the authenticated user to have the ``admin`` role.
+
+    Raises 403 if the user is not an admin.
+    """
+    if user.role != "admin":
+        raise HTTPException(
+            status_code=status.HTTP_403_FORBIDDEN,
+            detail="Admin access required",
+        )
+    return user
diff --git a/backend/app/core/exceptions.py b/backend/app/core/exceptions.py
new file mode 100644
index 0000000..62c8ae4
--- /dev/null
+++ b/backend/app/core/exceptions.py
@@ -0,0 +1,49 @@
+"""Domain-specific HTTP exceptions for the DAK Zweitmeinungs-Portal."""
+
+from fastapi import HTTPException, status
+
+
+class CaseNotFoundError(HTTPException):
+    """Raised when a requested case does not exist (404)."""
+
+    def __init__(self, detail: str = "Case not found") -> None:
+        super().__init__(status_code=status.HTTP_404_NOT_FOUND, detail=detail)
+
+
+class DuplicateCaseError(HTTPException):
+    """Raised when a case with the same identifier already exists (409)."""
+
+    def __init__(self, detail: str = "Case already exists") -> None:
+        super().__init__(status_code=status.HTTP_409_CONFLICT, detail=detail)
+
+
+class InvalidImportFileError(HTTPException):
+    """Raised when an uploaded import file is malformed or invalid (400)."""
+
+    def __init__(self, detail: str = "Invalid import file") -> None:
+        super().__init__(status_code=status.HTTP_400_BAD_REQUEST, detail=detail)
+
+
+class ICDValidationError(HTTPException):
+    """Raised when ICD code validation fails (422)."""
+
+    def __init__(self, detail: str = "ICD code validation failed") -> None:
+        super().__init__(
+            status_code=status.HTTP_422_UNPROCESSABLE_ENTITY, detail=detail
+        )
+
+
+class AccountLockedError(HTTPException):
+    """Raised when a user account is temporarily locked (423)."""
+
+    def __init__(self, detail: str = "Account is locked") -> None:
+        super().__init__(status_code=status.HTTP_423_LOCKED, detail=detail)
+
+
+class InvalidCredentialsError(HTTPException):
+    """Raised when login credentials are incorrect (401)."""
+
+    def __init__(self, detail: str = "Invalid credentials") -> None:
+        super().__init__(
+            status_code=status.HTTP_401_UNAUTHORIZED, detail=detail
+        )
diff --git a/backend/app/core/security.py b/backend/app/core/security.py
new file mode 100644
index 0000000..f171918
--- /dev/null
+++ b/backend/app/core/security.py
@@ -0,0 +1,114 @@
+"""Core security utilities: JWT, password hashing, MFA (TOTP)."""
+
+import hashlib
+import secrets
+from datetime import datetime, timedelta, timezone
+
+import pyotp
+from jose import jwt, JWTError  # noqa: F401 – re-exported for convenience
+
+# ---------------------------------------------------------------------------
+# Monkey-patch passlib for bcrypt >= 4.1 / 5.x compatibility.
+# Newer bcrypt removed ``__about__`` and rejects >72-byte passwords in its
+# internal wrap-bug detection.  The patch is applied before CryptContext is
+# instantiated so that passlib's backend initialisation succeeds.
+# ---------------------------------------------------------------------------
+import passlib.handlers.bcrypt as _bcrypt_mod  # noqa: E402
+
+_orig_finalize = _bcrypt_mod._BcryptBackend._finalize_backend_mixin.__func__  # type: ignore[attr-defined]
+
+
+@classmethod  # type: ignore[misc]
+def _patched_finalize(cls, name: str, dryrun: bool = False):  # type: ignore[no-untyped-def]
+    try:
+        return _orig_finalize(cls, name, dryrun)
+    except ValueError:
+        # bcrypt 4.1+ raises ValueError on >72-byte secrets during
+        # passlib's internal wrap-bug detection — safe to ignore.
+        return True
+
+
+_bcrypt_mod._BcryptBackend._finalize_backend_mixin = _patched_finalize  # type: ignore[assignment]
+# ---------------------------------------------------------------------------
+
+from passlib.context import CryptContext  # noqa: E402
+
+from app.config import get_settings
+
+settings = get_settings()
+
+pwd_context = CryptContext(schemes=["bcrypt"], deprecated="auto")
+
+
+# ---------------------------------------------------------------------------
+# Password hashing
+# ---------------------------------------------------------------------------
+
+def hash_password(password: str) -> str:
+    """Hash a plain-text password using bcrypt."""
+    return pwd_context.hash(password)
+
+
+def verify_password(plain: str, hashed: str) -> bool:
+    """Verify a plain-text password against a bcrypt hash."""
+    return pwd_context.verify(plain, hashed)
+
+
+# ---------------------------------------------------------------------------
+# JWT tokens
+# ---------------------------------------------------------------------------
+
+def create_access_token(user_id: int, role: str) -> str:
+    """Create a short-lived JWT access token."""
+    expire = datetime.now(timezone.utc) + timedelta(
+        minutes=settings.ACCESS_TOKEN_EXPIRE_MINUTES
+    )
+    payload = {
+        "sub": str(user_id),
+        "role": role,
+        "exp": expire,
+    }
+    return jwt.encode(
+        payload, settings.JWT_SECRET_KEY, algorithm=settings.JWT_ALGORITHM
+    )
+
+
+def create_refresh_token() -> str:
+    """Create a cryptographically secure refresh token (URL-safe)."""
+    return secrets.token_urlsafe(64)
+
+
+def hash_token(token: str) -> str:
+    """Return a SHA-256 hex digest of *token* (used for DB storage)."""
+    return hashlib.sha256(token.encode()).hexdigest()
+
+
+def decode_access_token(token: str) -> dict:
+    """Decode and validate a JWT access token.
+
+    Raises ``jose.JWTError`` on invalid or expired tokens.
+    """
+    return jwt.decode(
+        token, settings.JWT_SECRET_KEY, algorithms=[settings.JWT_ALGORITHM]
+    )
+
+
+# ---------------------------------------------------------------------------
+# MFA / TOTP
+# ---------------------------------------------------------------------------
+
+def generate_mfa_secret() -> str:
+    """Generate a new TOTP base-32 secret."""
+    return pyotp.random_base32()
+
+
+def verify_mfa_code(secret: str, code: str) -> bool:
+    """Verify a 6-digit TOTP code against *secret*."""
+    totp = pyotp.TOTP(secret)
+    return totp.verify(code)
+
+
+def get_mfa_uri(secret: str, email: str) -> str:
+    """Return an ``otpauth://`` provisioning URI for QR code generation."""
+    totp = pyotp.TOTP(secret)
+    return totp.provisioning_uri(name=email, issuer_name=settings.APP_NAME)
diff --git a/backend/tests/test_security.py b/backend/tests/test_security.py
new file mode 100644
index 0000000..15ad0cc
--- /dev/null
+++ b/backend/tests/test_security.py
@@ -0,0 +1,113 @@
+"""Tests for app.core.security — JWT, bcrypt, MFA/TOTP, token hashing."""
+
+import hashlib
+from datetime import datetime, timedelta, timezone
+
+import pyotp
+import pytest
+from jose import JWTError, jwt
+
+from app.config import get_settings
+from app.core.security import (
+    create_access_token,
+    create_refresh_token,
+    decode_access_token,
+    generate_mfa_secret,
+    get_mfa_uri,
+    hash_password,
+    hash_token,
+    verify_mfa_code,
+    verify_password,
+)
+
+settings = get_settings()
+
+
+# ---------------------------------------------------------------------------
+# Password hashing
+# ---------------------------------------------------------------------------
+
+def test_hash_and_verify_password():
+    """Hashing then verifying the same password returns True; wrong one False."""
+    hashed = hash_password("s3cret!")
+    assert verify_password("s3cret!", hashed) is True
+    assert verify_password("wrong-password", hashed) is False
+
+
+# ---------------------------------------------------------------------------
+# JWT access tokens
+# ---------------------------------------------------------------------------
+
+def test_create_and_decode_access_token():
+    """Round-trip: create a token and decode it, payload should match."""
+    token = create_access_token(user_id=1, role="admin")
+    payload = decode_access_token(token)
+    assert payload["sub"] == "1"
+    assert payload["role"] == "admin"
+    assert "exp" in payload
+
+
+def test_expired_token_raises():
+    """A token with a negative expiry must fail to decode."""
+    expire = datetime.now(timezone.utc) - timedelta(seconds=10)
+    token = jwt.encode(
+        {"sub": "1", "role": "admin", "exp": expire},
+        settings.JWT_SECRET_KEY,
+        algorithm=settings.JWT_ALGORITHM,
+    )
+    with pytest.raises(JWTError):
+        decode_access_token(token)
+
+
+def test_invalid_token_raises():
+    """Decoding a garbage string must raise JWTError."""
+    with pytest.raises(JWTError):
+        decode_access_token("not.a.valid.jwt.token")
+
+
+# ---------------------------------------------------------------------------
+# Refresh / hash tokens
+# ---------------------------------------------------------------------------
+
+def test_create_refresh_token_uniqueness():
+    """Two refresh tokens should never collide."""
+    t1 = create_refresh_token()
+    t2 = create_refresh_token()
+    assert t1 != t2
+    assert len(t1) > 40  # url-safe base64 of 64 bytes
+
+
+def test_hash_token():
+    """hash_token must produce a consistent SHA-256 hex digest."""
+    token = "test-token-value"
+    expected = hashlib.sha256(token.encode()).hexdigest()
+    assert hash_token(token) == expected
+    # Deterministic: calling twice yields the same result
+    assert hash_token(token) == hash_token(token)
+
+
+# ---------------------------------------------------------------------------
+# MFA / TOTP
+# ---------------------------------------------------------------------------
+
+def test_mfa_secret_and_verify():
+    """Generate a secret, produce the current OTP, verify it succeeds."""
+    secret = generate_mfa_secret()
+    assert len(secret) > 0
+    totp = pyotp.TOTP(secret)
+    current_code = totp.now()
+    assert verify_mfa_code(secret, current_code) is True
+
+
+def test_mfa_wrong_code():
+    """A clearly wrong code must be rejected."""
+    secret = generate_mfa_secret()
+    assert verify_mfa_code(secret, "000000") is False or verify_mfa_code(secret, "999999") is False
+
+
+def test_mfa_uri_format():
+    """The provisioning URI must start with the otpauth scheme."""
+    secret = generate_mfa_secret()
+    uri = get_mfa_uri(secret, "user@example.com")
+    assert uri.startswith("otpauth://totp/")
+    assert "user%40example.com" in uri or "user@example.com" in uri