- Encrypted messaging apps like Signal protect data in transit, but decrypted messages remain vulnerable on your device to forensic tools or malware.
- Despite strong encryption, devices are the weakest link—anyone with access to your phone can potentially read your Signal messages if they have the right tools.
- Default message retention settings create legal and compliance risks, as messages may be subject to discovery or subpoena long after they were sent.
In an era of data breaches, whistleblower leaks, and global surveillance, secure messaging apps like Signal have become the tool of choice for those who value privacy. From executives and attorneys to government officials, more professionals are turning to these apps to protect sensitive communications.
But there is a critical misunderstanding at the heart of this trust:
Encrypted does not mean invisible.
Even the most secure messages, once decrypted and displayed on your device, can become visible, accessible, and discoverable, especially in the hands of a skilled forensic examiner or if your device is unknowingly compromised.
This article explains how Signal works, what encryption protects, how data can still be exposed, and what legal, compliance, and technical professionals should consider when relying on secure messaging tools.
How Signal Secures Messages (In Plain English)
Signal uses end-to-end encryption (E2EE), meaning messages are encrypted on the sender’s device and decrypted only on the recipient’s device. No one, not even Signal’s servers, can read the message while it is in transit.
Behind the scenes, Signal uses:
- X3DH (Extended Triple Diffie-Hellman) to securely exchange keys between devices.
- Prekeys allow messages to be sent to users even when they are offline.
- The Double Ratchet Algorithm ensures that every message has a unique encryption key, so compromising one doesn’t expose the rest.
These tools create a shared secret key derived independently from each device. Importantly, the server never sees the private key nor transmits a decryption key. Instead, the devices compute the shared key using each other’s public keys.
This key generation happens instantly and invisibly for the user, but when a message is displayed, it exists in plain text on the screen.
What Encryption Protects
Encryption In Transit
This Signal capability is what most people understand: Signal ensures that messages are protected as they travel across the internet.
Encryption At Rest
Signal also encrypts messages stored on the phone, but that protection depends on the phone’s security, not Signal’s.
Once a device decrypts a message so the user can read it, that same decrypted message may be accessible to others with access to the device and its file system. And that is where things get risky.
Devices Are the Weakest Link
Despite the strength of Signal’s encryption, the device can be the point of failure, particularly during a legal or forensic investigation or if compromised by malicious actors.
On both Android and iOS:
- Signal stores messages and attachments in encrypted databases.
- The decryption keys are stored locally on the same device.
- If someone gains access to the full file system—via consent, a forensic tool, or a compromised operating system—they can often read messages just like the user.
Whether it is a forensic examiner using tools like Cellebrite Advanced or Magnet Forensics’ GrayKey or a bad actor using spyware, the privacy protections vanish if they can access the device at the file system level and the encryption keys. While Signal employs end-to-end encryption to secure messages in transit, once a message is received, it is stored in encrypted form on the device. However, because the encrypted message content and the local decryption keys are stored within the same file system, tools with sufficient access—such as forensic imaging software—can potentially decrypt and display message content on the fly. This access depends on the device’s state, encryption protections, and whether the keys are still accessible in memory or storage.
If you can read your Signal messages, so can anyone with access to your device.
The Invisible Threat: Compromised Devices
Not all message decryption comes from forensic labs. Some come in silent disguise.
A compromised device—infected with spyware or malware—can quietly monitor decrypted messages in real-time. This infection can happen through:
- Malicious apps or updates
- Clicking phishing links
- Insecure Wi-Fi networks
- Exploited OS vulnerabilities
- Rooted or jailbroken devices
This situation is dangerous because most users never know their device is compromised. Once the attacker is in, they can see everything Signal decrypts. The illusion of privacy holds—until it does not.
Message Retention: Legal Risk in Disguise
By default, Signal keeps messages on a device until the user manually deletes them or turns on the disappearing messages feature. While this can be convenient, it also introduces legal and privacy risks. Even when disappearing messages are enabled, they may stay on the device longer than expected, especially if the phone is turned off or the Signal app has not been opened. The messages will not be erased until Signal can run and process the deletion.
Risks of Unlimited Retention:
- Sensitive messages may linger for years, long after they are needed.
- Devices lost or repurposed may retain data that can be recovered later.
- Message history becomes a forensic record, even if not intended as one.
Legal Implications:
- Retained messages may be subject to subpoena or discovery.
- While useful for reducing exposure, auto-deletion features can complicate compliance with litigation holds or eDiscovery requirements if not understood and managed carefully.
Properly configured, Signal can support secure communication and legal defensibility—but that requires deliberate policy, not default settings.
Signal in Government: The Transparency Paradox
In early 2024, reporting revealed that White House and Pentagon staff increasingly used Signal for internal communication (source). While this reflects growing trust in secure messaging, it also raised red flags.
Under the Federal Records Act, communications by public officials may be subject to retention and transparency requirements. Apps like Signal, which lack institutional archiving features, can blur the line between personal privacy and professional accountability.
The same risk exists in corporate settings: security without governance invites failure to compliance.
Conclusion: The Illusion of Privacy Requires Clear Eyes
Signal’s encryption is strong, but it only protects messages in motion—not the devices they land on. In an era when professionals turn to secure messaging apps for confidentiality, it is easy to confuse encryption with invisibility. However, decrypted messages remain vulnerable once they appear on a device, whether through forensic tools, malware, or simple mismanagement of retention settings.
Privacy is not just about choosing the right app—it is about understanding how that app fits into a larger threat model. The safest communication still requires secure devices, clear policies, and a realistic understanding of what encryption can and cannot do.