Every mobile app should encrypt authentication credentials, payment information, personal identifying information, health data, location history, and any API keys or session tokens stored on the device or sent over the network. If your app collects it and a breach would embarrass you, harm a user, or violate a regulation, it needs encryption, both while it’s stored and while it’s moving between the app and your servers.

Encryption gets treated as a checkbox item far too often, “yes, we encrypt data,” without a clear answer to which data, where, and using what standard. That vagueness is exactly where breaches happen. A payment field encrypted correctly while an authentication token sits in plain text nearby is not a secure app, it’s an app with one obvious weak point instead of two.

This guide breaks down exactly what data belongs in each protection category, the specific algorithms and standards worth using in 2026, and where iOS and Android’s own secure storage systems fit into the picture. None of this requires inventing your own approach either. The platforms, and the broader security community, have already solved most of these problems, the actual work is implementing what’s already known to work correctly and consistently, not cutting corners on the data types that feel less obviously sensitive than a credit card number.

What Is Mobile App Encryption?

Mobile app encryption is the process of converting readable data into an unreadable format using a cryptographic algorithm, so that even if the data is intercepted or accessed without authorization, it can’t be read without the correct decryption key. This applies at two distinct points in a mobile app’s data lifecycle, while data sits stored on the device or on a server, and while it travels across a network between the app and a backend.

Why Encryption Matters More Than Most Teams Realize

Data breaches involving unencrypted or improperly encrypted data remain a leading cause of security incidents across industries, and mobile apps are a particularly attractive target since they routinely handle authentication credentials, payment details, and personal data on a device that can be lost, stolen, or compromised. IBM’s 2025 Cost of a Data Breach Report puts the global average cost of a breach at $4.44 million, though the US-specific average runs meaningfully higher at $10.22 million, a real financial argument for treating encryption as foundational, not optional.

The mobile-specific risk compounds this further. Unlike a server sitting in a controlled data center, a phone is physically carried into coffee shops, left in taxis, connected to public Wi-Fi, and occasionally lost or stolen outright. Every one of these ordinary situations is a potential access point to whatever data sits unencrypted on that device, which is precisely why mobile apps carry a genuinely different risk profile than a typical web application and why encryption deserves more deliberate attention here, not less.

Encryption at Rest vs Encryption in Transit

Encryption at Rest Is Defined As

Encryption at rest protects data while it’s stored, on the device itself, in a local database, or on a server, so that anyone gaining unauthorized access to the storage medium directly still can’t read the actual data without the decryption key.

Encryption in Transit Is Defined As

Encryption in transit protects data while it’s actively moving between two points, typically between the mobile app and a backend server, so that anyone intercepting the network traffic sees only encrypted, unreadable data rather than the actual content being transmitted.

Both are required, not optional alternatives to each other. Data encrypted at rest but transmitted in plain text is still exposed the moment it leaves the device, and data encrypted in transit but stored insecurely is still exposed the moment someone gains access to the device or database directly. Treating either one as sufficient on its own is one of the most common gaps in an otherwise reasonable security implementation, since it’s genuinely easy to get one half right, implement HTTPS everywhere, and assume the job is done, without realizing the local database or cached files still hold the same sensitive data completely unprotected.

What Data Should Be Encrypted in a Mobile App?

Authentication Credentials and Session Tokens

Passwords should never be stored directly, even encrypted, they should be hashed using a dedicated password hashing function like Argon2 or bcrypt, which are specifically designed to resist brute-force attacks. Session tokens and API keys, which grant ongoing access without requiring a password re-entry, need encryption at rest just as much as the password itself, since a leaked session token can be just as damaging as a leaked password.

Personal Identifying Information (PII)

Names, addresses, phone numbers, email addresses, government ID numbers, and any other data that can identify a specific individual need encryption both at rest and in transit, and this category is where most privacy regulations, GDPR and CCPA among them, focus their strictest requirements.

Payment and Financial Data

Credit card numbers, bank account details, and transaction history require encryption to a standard that satisfies PCI-DSS compliance if your app processes payments directly, and in practice, most apps are better served by tokenizing payment data through a processor like Stripe rather than storing raw card details at all.

Health and Medical Data

Any data tied to a user’s health, symptoms logged, medical history, biometric health readings, falls under HIPAA in the US if your app touches protected health information, and the encryption bar here is generally the highest of any data category given both the sensitivity and the regulatory consequences of a breach.

Location Data

Location history reveals genuinely sensitive patterns about a person, where they live, work, worship, or seek medical care, and it deserves encryption at rest even when it doesn’t fall under a specific named regulation, since the privacy harm from exposure is real regardless of legal classification.

Biometric Data

Fingerprint data, facial recognition data, and other biometric identifiers are uniquely sensitive because, unlike a password, a user can’t change their fingerprint after a breach, which is why biometric data should stay on-device within the platform’s secure hardware enclave whenever possible rather than being transmitted or stored server-side at all.

This is worth calling out as a genuinely different security posture than most other data categories. For nearly every other data type covered here, the question is which encryption standard to apply to storage and transmission. For biometric data, the more defensible answer is often to avoid transmitting or centrally storing it at all, letting the device’s own secure hardware, Face ID’s Secure Enclave, Android’s equivalent hardware-backed biometric storage, handle the actual matching locally and simply return a pass or fail result to the app, never the raw biometric data itself.

Encryption Standards You Should Actually Use

Approved Algorithms and Protocols

Use AES-256, specifically AES-256-GCM, for encrypting stored data, and TLS 1.3 for all network communication, since both represent the current, vetted standard recommended across NIST guidance and mobile security frameworks. For password hashing specifically, use Argon2 as the current best practice, with bcrypt as a solid, well-established alternative, rather than a general-purpose hash function that wasn’t designed to resist brute-force attacks.

What to Avoid

• DES and 3DES, both outdated symmetric encryption algorithms with known weaknesses.
• RC4, a stream cipher with well-documented vulnerabilities.
• MD5 and SHA-1, both considered cryptographically broken for security purposes.
• ECB mode, an encryption mode that leaves patterns visible in the encrypted output, undermining the point of encrypting in the first place.
• Rolling your own encryption. Custom, homegrown cryptographic implementations consistently introduce vulnerabilities that established, peer-reviewed algorithms have already solved.

iOS Keychain vs Android Keystore

Neither platform’s secure storage should hold your encryption keys in application code or in a standard file. Apple’s Keychain Services documentation and Android’s Keystore documentation both confirm this is the intended, hardware-backed pattern each platform provides specifically to keep keys secure even if the broader OS is compromised.

Implementing Encryption Correctly in Your App

Getting encryption right isn’t just picking the correct algorithm, it’s implementing key management, certificate pinning, and secure storage correctly across every place sensitive data touches your app, which is exactly where a lot of otherwise well-intentioned implementations fall short. Following the OWASP Mobile Top 10 as a structured reference catches the most common real-world implementation mistakes, insecure data storage, inadequate transport layer protection, and hardcoded cryptographic keys chief among them. If your app handles genuinely sensitive data and you want encryption implemented correctly across every layer, not just the parts that are easy to test, our mobile app development team builds this in as core architecture from the start rather than retrofitting it before an audit.

Encryption and Regulatory Compliance

GDPR requires encryption as one of several “appropriate technical measures” for protecting personal data of EU residents, though it doesn’t mandate one specific algorithm, the standard is that your protection is genuinely adequate for the sensitivity of the data involved. HIPAA in the US similarly requires encryption of protected health information both at rest and in transit for covered entities, with specific penalties tied to breaches involving inadequately protected data. PCI-DSS, the standard covering payment card data, is more prescriptive, requiring strong cryptography for cardholder data both stored and transmitted, which is a major reason most apps tokenize payment data through a processor rather than handling raw card numbers directly.

None of these regulations exist in isolation from the technical practices covered above, meeting compliance requirements and following genuinely good encryption practice are, in nearly every case, the same underlying work. This is a genuinely useful way to think about compliance in practice: instead of treating GDPR, HIPAA, and PCI-DSS as three separate checklists to satisfy independently, building encryption correctly against the standards covered earlier in this guide, AES-256 at rest, TLS 1.3 in transit, proper key management, tends to satisfy the substance of all three simultaneously, since they’re all pointing at the same underlying goal of genuinely protecting sensitive data rather than three unrelated sets of technical requirements.

Common Mobile App Encryption Mistakes

• Encrypting some sensitive data but not all of it. A payment field encrypted correctly while an authentication token sits exposed nearby still leaves a real attack surface.
• Hardcoding encryption keys in application source code. Keys embedded in the app binary can be extracted through reverse engineering, defeating the encryption entirely.
• Using outdated algorithms because old documentation or tutorials still reference them. DES, MD5, and SHA-1 continue showing up in older guides despite being cryptographically broken for security purposes.
• Encrypting data at rest but skipping certificate pinning for network traffic. Without certificate pinning, a compromised or malicious certificate authority can still enable interception even over an encrypted connection.
• Storing passwords with reversible encryption instead of proper hashing. Passwords should be hashed with Argon2 or bcrypt, never stored in any form that could be decrypted back to the original value.
• Assuming app store approval means the app is secure. App store review checks for malware and policy violations, not architectural encryption flaws, so passing review is not a security guarantee.

For a broader view of how encryption fits into overall mobile security practice, our guide to mobile app security best practices covers the surrounding controls, authentication, API security, and secure coding practices, that encryption works alongside rather than in isolation.

Building Encryption Into Your App the Right Way

Encryption that’s implemented inconsistently, strong on one data type, weak or missing on another, provides a false sense of security that’s arguably worse than knowing exactly where your gaps are. A breach report that reveals “the payment data was encrypted, but the attacker got in through an unencrypted session token” doesn’t read any better to a user or a regulator than no encryption at all, since the actual harm, the breach itself, still happened. If you’re building a new app or reviewing an existing one for genuine data protection, get in touch with our team and we’ll walk through exactly what your app handles and how it should be protected.

Frequently Asked Questions