Data in transit

Data in transit, also referred to as data in motion, encompasses any digital information actively transferred over a network or communication channel from one endpoint to another, such as during web browsing, email transmission, or file sharing.^[1] This state contrasts with data at rest (stored statically) and data in use (being processed), forming one of the three core phases of data lifecycle as defined in the NIST Cybersecurity Framework 2.0.^[2] Protecting data in transit is essential for maintaining confidentiality, integrity, and availability, particularly in an era of widespread network connectivity and cyber threats.^[3] Without safeguards, transmitted data faces significant risks, including interception by unauthorized parties through eavesdropping, packet sniffing, or man-in-the-middle attacks, which can result in data theft, alteration, or exposure of sensitive details like personal identifiers or financial records.^[4] For example, unencrypted transfers in critical sectors, such as election systems, can jeopardize operational integrity by allowing adversaries to access ballot files or voter data mid-transmission.^[1] Encryption serves as the cornerstone of data-in-transit security, transforming readable data into an unreadable format accessible only to authorized recipients with the proper decryption key.^[3] The predominant protocol for this purpose is Transport Layer Security (TLS), which provides end-to-end protection by combining symmetric and asymmetric cryptography to ensure secure key exchange, data confidentiality, and tamper detection.^[3] Federal guidelines, such as those in NIST Special Publication 800-52 Revision 2, recommend implementing TLS 1.2 or 1.3 exclusively, while deprecating older versions like TLS 1.0 and 1.1 due to known vulnerabilities.^[3] Complementary practices include using secure protocols like HTTPS for web communications, SFTP or SCP for file transfers, and SSH for remote access, alongside regular certificate validation and enforcement of encryption in vendor agreements.^[1]

Overview

Definition

Data in transit refers to digital information that is actively moving from one location to another, such as over networks, wireless connections, or between devices and systems.^[5] This includes both structured and unstructured data transmitted across the internet, private networks, or directly between endpoints like client-server interactions.^[5] Unlike data at rest, which resides statically on storage media such as hard drives or databases, data in transit is inherently ephemeral, existing only during the transfer process.^[6] Key characteristics of data in transit include its temporary nature and vulnerability to exposure at intermediary points along the transmission path, such as routers, physical cables, or wireless airwaves.^[7] These points represent potential access opportunities during the data's journey from sender to receiver, distinguishing it from more controlled static storage environments.^[6] The dynamic flow of data in this state underscores its reliance on underlying communication infrastructures for reliable delivery. Common contexts for data in transit encompass everyday networked activities, including email transmission over protocols like SMTP, web browsing via HTTP or HTTPS, file transfers using FTP or SFTP, and API calls exchanging information between applications.^[4] The concept of data in transit emerged alongside the rise of networked computing in the late 1960s and 1970s, particularly with the development of ARPANET by the U.S. Department of Defense's Advanced Research Projects Agency (ARPA).^[8] ARPANET, which became operational in 1969, introduced packet-switching technology that enabled the transmission of data between geographically dispersed computers, laying the foundation for modern internet protocols in the 1980s.^[8]

Importance in Information Security

Securing data in transit plays a pivotal role in upholding the confidentiality pillar of the CIA triad—confidentiality, integrity, and availability—in information security frameworks. By protecting data as it moves between systems, networks, or endpoints, organizations prevent unauthorized interception or disclosure that could compromise sensitive information, thereby averting potential data breaches and ensuring that only authorized parties access transmitted content. This is particularly emphasized in NIST guidelines, which highlight confidentiality as essential to safeguarding data against eavesdropping during transmission.^[9] Beyond core security principles, securing data in transit is integral to regulatory compliance, serving as a foundational requirement under frameworks like the General Data Protection Regulation (GDPR) and the Health Insurance Portability and Accountability Act (HIPAA). GDPR's Article 32 mandates technical measures, such as encryption, to ensure secure transmission of personal data, with non-compliance potentially resulting in fines up to 4% of global annual turnover or €20 million, whichever is greater. Similarly, HIPAA's Security Rule requires transmission security standards to protect electronic protected health information (ePHI) in transit, where violations can lead to penalties exceeding $1.5 million per year. These regulations underscore how unsecured data transit not only exposes organizations to legal penalties but also undermines trust in data handling practices. The 2025 Verizon Data Breach Investigations Report analyzed 12,195 breaches and found vulnerability exploitation involved in 20% of them, highlighting persistent risks from network vulnerabilities that can affect data in transit.^[10] The economic ramifications of failing to secure data in transit are substantial, amplifying the urgency of proactive measures. More broadly, IBM's 2025 Cost of a Data Breach Report indicates that the global average cost of a data breach reached $4.44 million as of 2025.^[11] These figures emphasize how transit security forms a critical line of defense against financially devastating exposures.

Threats

Eavesdropping and Interception

Eavesdropping and interception represent passive threats to data in transit, where unauthorized parties capture communications without altering or disrupting them. These attacks exploit the inherent openness of network transmission mediums, allowing attackers to monitor unencrypted or poorly protected data streams. In shared network environments, such as those using broadcast protocols, any connected device can potentially access packets intended for others, enabling the collection of sensitive information like login credentials, personal messages, or financial details.^[12] The primary mechanism involves the use of packet sniffing tools to capture and analyze network traffic. Tools like Wireshark, an open-source network protocol analyzer, allow users to intercept and inspect packets in real time on local networks, revealing contents if not encrypted. On shared mediums, attackers place their devices in promiscuous mode to receive all traffic, not just their own, facilitating the extraction of plaintext data from protocols like HTTP or unencrypted email.^[13] Common scenarios include Wi-Fi sniffing in public hotspots, where open or weakly secured access points broadcast data visible to nearby devices equipped with sniffing capabilities. In wired networks, physical cable tapping—such as splicing into Ethernet or fiber optic lines—permits direct interception of signals without network authorization. At the ISP level, service providers or intermediaries with access to backbone infrastructure can monitor aggregated traffic flows, capturing data en route between endpoints.^[14]^[15]^[16] Historical examples underscore the persistent concerns over government-facilitated eavesdropping. The 1994 Clipper chip controversy arose when the U.S. government proposed embedding a backdoor in encryption hardware for telecommunications devices, allowing law enforcement to decrypt communications via escrow-held keys, sparking debates on privacy versus surveillance. In 2013, Edward Snowden's revelations exposed the NSA's PRISM program, which intercepted data in transit from major tech firms and ISPs, collecting vast amounts of user communications under broad authorities. More recently, as of 2025, the Salt Typhoon campaign—a Chinese state-sponsored operation—compromised U.S. telecommunications providers, enabling interception of unencrypted voice and internet traffic for espionage purposes.^[17]^[18]^[19] Detection of such passive attacks poses significant challenges, as they generate no anomalous traffic or modifications detectable by standard endpoint monitoring. Attackers operate silently, often from external positions without network integration, leaving no traces like altered timestamps or error logs. Without specialized tools such as traffic anomaly detectors or honeypots, these interceptions remain undetectable, complicating forensic attribution.^[20]^[21]

Man-in-the-Middle Attacks

A man-in-the-middle (MITM) attack involves an adversary secretly positioning themselves between two communicating parties to intercept, relay, or alter data in transit, often without the knowledge of the endpoints. The attacker typically relays messages between the victim and the legitimate destination while simultaneously eavesdropping or modifying the content, creating the illusion of direct communication. Common techniques include ARP spoofing, where the attacker sends forged ARP messages to associate their MAC address with the IP address of a legitimate host, thereby redirecting traffic through their device, and DNS poisoning, which manipulates DNS responses to redirect users to malicious servers controlled by the attacker. These methods enable the attacker to control the flow of data, combining passive observation—similar to basic eavesdropping—with active interference.^[22]^[23]^[24] MITM attacks manifest in various types, each exploiting specific weaknesses in network or application layers. Session hijacking occurs when an attacker steals or predicts a valid session token, allowing them to impersonate the user and take over an active session to access sensitive information or perform unauthorized actions. Another variant is SSL stripping, where the attacker intercepts TLS handshakes to downgrade a secure HTTPS connection to unencrypted HTTP, exposing data that would otherwise be protected during transmission. These types rely on the attacker's ability to insert themselves into the communication path, often leveraging unencrypted protocols or flawed authentication mechanisms.^[25]^[24] Real-world incidents highlight the potency of MITM attacks in compromising data in transit. In 2014, the OpenSSL CCS injection vulnerability (CVE-2014-0224) allowed attackers to perform MITM exploits by injecting arbitrary content during TLS handshakes, potentially disclosing credentials or enabling impersonation of victims. As of 2025, the Salt Typhoon campaign has also employed MITM techniques by compromising telecom infrastructure to intercept and manipulate communications between users and services. Such attacks have demonstrated the feasibility of exploiting trusted channels for unauthorized access.^[26]^[19] The consequences of successful MITM attacks are severe, often resulting in data theft, such as the unauthorized extraction of login credentials, financial details, or personal information transmitted between parties. Attackers can also inject malware into the communication stream, compromising endpoints or propagating further infections across networks. Additionally, these attacks enable credential compromise, where stolen authentication tokens allow sustained unauthorized access, leading to broader breaches like account takeovers or operational disruptions.^[24]^[27]^[28]

Protection Methods

Encryption Techniques

Encryption techniques for protecting data in transit primarily involve cryptographic algorithms that transform plaintext into ciphertext, rendering it unintelligible to unauthorized parties such as those attempting eavesdropping.^[29] These methods rely on two core approaches: symmetric encryption, which uses a single shared key for both encryption and decryption, and asymmetric encryption, which employs a pair of keys—a public key for encryption and a private key for decryption.^[30] Symmetric encryption, exemplified by the Advanced Encryption Standard (AES), is favored for bulk data transmission due to its efficiency in handling large volumes of information.^[31] In contrast, asymmetric encryption, such as the RSA algorithm developed by Rivest, Shamir, and Adleman, is typically used for secure key exchange to establish a shared symmetric key without prior secret distribution.^[32] The key processes in applying these techniques to data in transit begin with an initial handshake phase, where asymmetric encryption facilitates the negotiation of a temporary symmetric session key between communicating parties.^[33] Once established, this session key is used to encrypt the actual payloads of data transmitted over the channel, ensuring that only the intended recipient can decrypt and access the original content. For symmetric ciphers like AES, which operates on fixed-size blocks of 128 bits, various modes of operation define how data is processed to achieve security properties such as confidentiality and integrity. Common modes include Cipher Block Chaining (CBC), which links each plaintext block to the previous ciphertext block via an initialization vector to prevent identical plaintext blocks from producing identical ciphertext, and Galois/Counter Mode (GCM), which provides both encryption and authentication in a single pass, using a counter for parallelism and a Galois field multiplier for tag generation.^[29]^[33] The fundamental mathematical representation of these processes is the encryption function C = E(M, K), where M represents the plaintext message, K the secret key, and C the resulting ciphertext, with decryption reversing this via M = D(C, K).^[30] This symmetric model assumes the key remains confidential to authorized parties, while asymmetric variants, like RSA, leverage modular exponentiation for public-key operations: ciphertext is computed as C = M^e \mod n using the public exponent e and modulus n, with decryption M = C^d \mod n using the private exponent d.^[32] The evolution of these techniques reflects advancing computational threats and standards. The Data Encryption Standard (DES), adopted in 1977 as FIPS 46, was the first widely used symmetric block cipher but became deprecated due to its 56-bit key length vulnerability to brute-force attacks by the late 1990s.^[34] It was succeeded by AES in 2001 under FIPS 197, which supports key lengths of 128, 192, or 256 bits for robust protection of transmitted data.^[30] Looking ahead, concerns over quantum computing have driven the development of quantum-resistant alternatives, including lattice-based cryptography, with NIST standardizing algorithms like ML-KEM (based on module-lattice problems) in FIPS 203 as of 2024 to safeguard data in transit against future quantum threats. In March 2025, NIST selected HQC, a code-based key-encapsulation mechanism, as an additional algorithm for standardization to provide further quantum-resistant options for key exchange in data transmission.^[35]^[36]

Secure Transmission Protocols

Secure transmission protocols provide standardized mechanisms to protect data in transit by ensuring confidentiality, integrity, and authenticity through layered security over network connections. These protocols integrate cryptographic techniques to establish secure channels, preventing unauthorized access during transmission. Key examples include the Transport Layer Security (TLS) protocol, which succeeded the earlier Secure Sockets Layer (SSL) and has evolved through versions 1.0 to 1.3, and the IP Security (IPsec) protocol suite designed for securing IP communications, particularly in virtual private networks (VPNs).^[37]^[38]^[39] TLS operates at the transport layer and begins with a handshake process to negotiate security parameters and establish session keys. The process starts with the client sending a ClientHello message containing supported cipher suites, protocol versions, and a random nonce; the server responds with a ServerHello selecting parameters, followed by its digital certificate for authentication, and a key exchange message to derive shared secrets using ephemeral Diffie-Hellman exchanges for forward secrecy. In TLS 1.3, finalized in 2018, this handshake is streamlined to a single round trip, mandating forward secrecy to ensure that compromised long-term keys do not expose past sessions.^[37]^[37]^[37] Common use cases for TLS include securing web traffic via HTTPS, where HTTP is layered over TLS to protect browser-server interactions such as login credentials and sensitive data exchanges. Additionally, the Secure Shell (SSH) protocol employs TLS-like mechanisms for remote access, enabling encrypted command execution and tunneling over insecure networks. For secure file transfer, the SSH File Transfer Protocol (SFTP) extends SSH to provide authenticated and encrypted file operations, supporting commands like upload, download, and directory listing.^[40] IPsec secures data at the network layer through two primary modes: transport mode, which encrypts only the payload of IP packets to protect end-to-end communications between hosts, and tunnel mode, which encapsulates the entire IP packet within a new IP header for gateway-to-gateway VPNs, hiding the original source and destination. This architecture allows IPsec to integrate seamlessly with existing IP infrastructure, providing security for site-to-site connections without modifying application protocols.^[39]^[39] Recent developments include the QUIC protocol, standardized in 2021 as the foundation for HTTP/3, which embeds TLS 1.3 directly into its UDP-based transport to enable faster handshakes and multiplexing while maintaining encryption for all traffic, reducing latency in web applications compared to traditional TCP-based protocols.^[41]^[42]

Standards and Best Practices

Key Standards

The Internet Engineering Task Force (IETF) plays a central role in standardizing protocols for secure data transmission through its Request for Comments (RFC) series, notably RFC 8446, which defines Transport Layer Security (TLS) version 1.3 for protecting data in transit over the internet.^[37] The National Institute of Standards and Technology (NIST) establishes cryptographic standards via Federal Information Processing Standards (FIPS), including FIPS 140-3, approved in March 2019 and effective from September 2019, which specifies security requirements for cryptographic modules used in transit protection.^[43] Additionally, the International Organization for Standardization (ISO) and the International Electrotechnical Commission (IEC) through ISO/IEC 27001:2022 provide a framework for information security management systems (ISMS), with Annex A control 8.24 on the use of cryptography mandating rules for protecting confidentiality and integrity of data in transit.^[44] Specific standards address sector-specific needs for data in transit. The Payment Card Industry Data Security Standard (PCI DSS) version 4.0, released in March 2022, requires strong cryptography—such as TLS 1.2 or higher—for encrypting cardholder data during transmission over open, public networks under Requirement 4.^[45] The Open Web Application Security Project (OWASP) offers guidelines in its Secure Coding Practices Quick Reference Guide, recommending TLS encryption for all sensitive information transmission, including validation of certificates to prevent insecure protocols.^[46] Historical milestones trace the evolution of these standards. Secure Sockets Layer (SSL) version 1.0, developed by Netscape in 1994, was never publicly released due to significant security flaws, marking an early but aborted effort in transit encryption.^[47] TLS 1.0 emerged in 1999 via IETF RFC 2246 as an upgrade from SSL 3.0, providing a standardized protocol for privacy and data integrity over the internet.^[48] More recently, NIST selected CRYSTALS-Kyber in August 2024 as a key encapsulation mechanism in FIPS 203 for post-quantum cryptography, addressing future threats to transit encryption from quantum computing.^[49] Global variations include the European Union's eIDAS Regulation (EU) No 910/2014, effective since 2016 and updated via Regulation (EU) 2024/1183 entering force in May 2024, which mandates qualified electronic certificates for trust services to ensure secure authentication and signatures in cross-border data transit.^[50]

Implementation Guidelines

Implementing protections for data in transit requires a structured approach that aligns with established security standards to ensure compliance and effectiveness. Organizations should begin by enforcing the use of TLS 1.3 as the minimum protocol version across all endpoints, as it provides enhanced security features like improved forward secrecy and reduced vulnerability to certain attacks compared to earlier versions.^[51] For web-based communications, implementing HTTP Strict Transport Security (HSTS) is essential, which instructs browsers to interact only over HTTPS and prevents protocol downgrade attacks by specifying directives such as max-age and includeSubDomains.^[52] Effective certificate management further strengthens these measures; tools like Let's Encrypt, which began issuing certificates in July 2015, automate the issuance and renewal of free TLS certificates, simplifying deployment for large-scale environments.^[53] To deploy these protections, organizations must follow key steps starting with network assessment. Tools such as Nmap can be used to scan for open ports, identify active services, and detect unencrypted traffic flows, providing a baseline for vulnerabilities in data transmission paths.^[54] Endpoint configuration follows, where administrators disable weak ciphers—such as those using RC4 or MD5—and prioritize strong suites like AES-GCM to align with modern security requirements.^[55] Ongoing monitoring is critical, utilizing Security Information and Event Management (SIEM) tools to aggregate logs from network devices and analyze patterns in TLS-encrypted traffic for anomalies, such as unexpected certificate changes or volume spikes indicative of threats. Despite these practices, implementation faces notable challenges, particularly with legacy systems. Many older devices and applications still rely on TLS 1.0, which lacks robust security and exposes data to interception; upgrading requires careful compatibility testing to avoid service disruptions, often involving phased migrations or virtual patching.^[56] Encryption also introduces performance overhead, as the computational demands of key exchanges and data transformation can reduce throughput by 10-20% on software-only implementations; this is commonly mitigated through hardware acceleration, such as Intel's AES-NI instructions, which offload processing to specialized CPU extensions for near-native speeds.^[57] A prominent example of successful large-scale implementation is Google's 2014 "HTTPS Everywhere" initiative, announced in August of that year, which integrated HTTPS as a search ranking signal to incentivize adoption across the web. This effort significantly boosted global HTTPS usage—from under 30% of page loads in 2014 to over 90% by 2020—thereby reducing interception risks for billions of daily users by enforcing encrypted transit by default.^[58]