Symmetric vs Asymmetric Encryption Explained (2026)

Symmetric vs Asymmetric Encryption: The Short Answer

Symmetric encryption uses one shared key to both lock and unlock data, while asymmetric encryption uses a mathematically linked pair of keys, a public key anyone can use to encrypt and a private key only the recipient holds to decrypt. Symmetric encryption is faster and better suited to encrypting large amounts of data at rest, such as files on a server or an entire laptop hard drive. Asymmetric encryption is slower but solves a problem symmetric encryption can't: securely exchanging a key with someone you've never met, which is why it underpins HTTPS, digital signatures, and secure email. Most real-world systems, including the browser padlock on the page you're reading right now, use both together.

How Symmetric Encryption Works

Symmetric encryption scrambles data using an algorithm and a single secret key, and that same key reverses the process to decrypt it. Whoever holds the key can both encrypt and decrypt, which means the key itself has to be protected and shared only with people who need it.

The current standard is the Advanced Encryption Standard (AES), a symmetric algorithm adopted by the National Institute of Standards and Technology (NIST) in 2001. AES-256, which uses a 256-bit key, is the version most security tools default to today, including full-disk encryption features like BitLocker and FileVault, and encrypted backup software. Because there's only one key to process through the math, symmetric encryption is computationally fast, which is why it's used for large volumes of data: databasesencrypted backups, and entire hard drives.

The tradeoff is key distribution. If you encrypt a file with a symmetric key and need to send that file to someone else, you also have to get them the key, and if that key is intercepted in transit, the encryption protects nothing. That's the exact problem asymmetric encryption was designed to solve.

How Asymmetric Encryption Works

Asymmetric encryption, also called public-key cryptography, uses two mathematically related keys: a public key that can be shared openly and a private key that never leaves its owner's device. Data encrypted with the public key can only be decrypted with the matching private key, so anyone can send a business a secure message without ever needing a shared secret arranged in advance.

The two most common asymmetric algorithms are RSA (Rivest-Shamir-Adleman) and elliptic curve cryptography (ECC). NIST's guidance in Special Publication 800-131A phased out 1024-bit RSA keys and now calls for a minimum 2048-bit RSA key, or the ECC equivalent, a benchmark most commercial security tools follow as well. ECC delivers comparable security with a smaller key size, part of why it has become standard on mobile devices and modern browsers.

Asymmetric encryption also enables digital signatures: signing data with a private key lets anyone holding the matching public key verify it came from you and wasn't altered afterward, which is the basis for code-signing certificates and secure email signing.

The tradeoff is speed. The math behind public-key cryptography is far more computationally expensive than symmetric encryption, so using it to encrypt large files or high volumes of data would be noticeably slower and more resource-intensive.

Why HTTPS Uses Both Types of Encryption

When you connect to a website secured with Transport Layer Security (TLS), the protocol behind the padlock icon in your browser's address bar, your browser and the server first use asymmetric encryption to verify the site's identity and agree on a temporary symmetric key. Once that key exchange finishes, the connection switches to symmetric encryption, typically AES, for the rest of the session, because it moves data quickly without the overhead of public-key math on every packet.

This hybrid model shows up everywhere in practice. Encrypted email standards like S/MIME and PGP use a recipient's public key to encrypt a one-time symmetric key, then encrypt the actual message with that faster symmetric key. VPN tunnels work the same way. Password managers and full-disk encryption tools, by contrast, use symmetric encryption alone, because there's no key exchange to solve, you're protecting your own data with your own passphrase.

This is also why encryption protects confidentiality, one leg of the CIA triad of confidentiality, integrity, and availability, but only if the underlying keys are managed correctly. Key management gaps are a common finding during a vulnerability assessment, and they're easy to miss if you assume encryption is a one-time setup rather than an ongoing control.

How This Fits Into Your Compliance Obligations

Encryption is one of the specific controls regulators expect security-conscious businesses to have in place, not just a background feature. Under the FTC Safeguards Rule, financial institutions, a category that includes tax preparers and accounting firms, must encrypt customer information at rest and in transit or document why an equivalent control is in place; the rule also requires designating a qualified individual responsible for the security program. The IRS reinforces this in its Security Six checklist for tax professionals, which lists data encryption alongside antivirus software, firewalls, and multi-factor authentication as baseline protections.

None of this means encryption alone satisfies your obligations. If a laptop with an encrypted hard drive is stolen while logged in and unlocked, the encryption doesn't help, because the data was already accessible at the moment of theft. And if you ever discover that an encryption key, password, or credential has actually been exposed, treat it as a security incident and follow a documented incident response framework rather than assuming the exposure is contained. Specific compliance questions for your practice should be reviewed with legal counsel.

What This Means for Your Written Information Security Plan

You rarely need to choose between symmetric and asymmetric encryption directly, because the software you already use, your operating system, backup provider, and email platform, makes that choice for you behind the scenes. Your responsibility is confirming those settings are turned on, applied consistently across every device, and documented as part of a broader data protection program.

For accounting and tax practices, that documentation belongs in a written information security plan. Bellator Cyber Guard builds a custom WISP starting at $749 for practices with up to 5 users, with larger practices quoted separately, and most firms find it saves 20 to 40 billable hours compared to drafting a plan from scratch.