SSH key comparison exposes the governance gap in access management

At a glance

What this is: This is a guide to SSH key types and management practices, with the key finding that secure authentication depends as much on governance as on the algorithm itself.

Why it matters: It matters because SSH keys are non-human identities in practice, and IAM teams need visibility, rotation, offboarding, and access control patterns that work across server access, service accounts, and privileged workflows.

By the numbers:

• 96% of organisations store secrets outside of secrets managers in vulnerable locations including code, config files, and CI/CD tools.
• Only 20% have formal processes for offboarding and revoking API keys, and even fewer have procedures for rotating them.
• Only 5.7% of organisations have full visibility into their service accounts.

👉 Read StrongDM's guide to SSH key comparison and access management

Context

SSH keys are a non-human identity mechanism, not just a login convenience. They are meant to prove possession of a private key without passwords, but the governance problem starts when keys are distributed manually, left untracked, or never revoked after access changes. For IAM teams, that makes SSH a lifecycle and privilege-control issue, not only a cryptography choice.

The article focuses on algorithm comparison, yet the more durable security question is who owns each key, how it is rotated, and when it is removed. That is the same structural problem seen across service accounts and other machine identities, which is why the Ultimate Guide to NHIs remains the clearest baseline for the lifecycle controls SSH deployments depend on.

Key questions

Q: How should security teams govern SSH keys in cloud and server environments?

A: Treat SSH keys as governed non-human identities. Assign an owner, define an expiry or rotation interval, track where the key is trusted, and revoke it when the access relationship ends. The key control is lifecycle discipline, because an unused but valid key is still an active credential. Central visibility matters as much as the algorithm choice.

Q: Why do SSH keys create risk when they are not rotated or revoked?

A: Because the credential persists even after the original business need has changed. A valid private key can continue to authenticate to any server that still trusts the matching public key, which extends the attack window and increases blast radius. That is why key rotation and offboarding are governance controls, not administrative chores.

Q: What breaks when SSH keys are managed manually across many systems?

A: Manual management breaks inventory accuracy, ownership clarity, and timely revocation. Keys get copied, forgotten, and left behind on servers that no one actively reviews. The result is access sprawl, especially in environments with contractors, automation, or many ephemeral servers. Visibility and central control are the first things that fail.

Q: Should organisations treat SSH access as part of PAM and access review programmes?

A: Yes. SSH is privileged access whenever it reaches production systems, infrastructure, or sensitive data paths. If it is excluded from PAM and access review processes, teams miss a major non-human identity channel that can persist for months. The right frame is governance of privileged machine access, not just secure remote login.

Technical breakdown

SSH public-private key pairs and authentication flow

SSH authentication relies on asymmetric cryptography. The public key is stored on the server, while the private key stays with the client and signs or proves possession during connection. This removes password guessing from the path, but it does not remove identity governance. The key itself becomes the credential, which means the main controls shift to issuance, storage, rotation, and revocation. In practice, the security value of SSH depends on whether the private key remains protected and whether the server-side authorized_keys state matches the intended access model.

Practical implication: treat each SSH key pair as a governed NHI credential with ownership, expiry, and revocation requirements.

RSA, DSA, and ECDSA key choices

The article contrasts three algorithms that differ mainly in compatibility, signature approach, and key size efficiency. RSA remains widely used but depends on larger key sizes for stronger security. DSA is historically important but less attractive for modern deployments, while ECDSA offers shorter keys with comparable security characteristics when elliptic curve parameters are chosen carefully. From an IAM perspective, algorithm selection matters less than lifecycle discipline, because a strong algorithm does not compensate for a stale, shared, or unrevoked key.

Practical implication: standardise on approved algorithms, but pair that standard with explicit key retirement and reissue processes.

SSH key management, rotation, and revocation

The operational weakness in SSH is rarely the cryptography itself. It is the control plane around key distribution, tracking, and timely revocation. Manual administration scales poorly because keys accumulate across hosts, users, and automation paths. Centralised management, auditing, and role-based access help, but only when they are tied to actual key ownership and offboarding events. SSH therefore behaves like every other NHI system: the credential is durable, the risk is persistent, and the programme fails when revocation lags behind access change.

Practical implication: build SSH key inventory, revocation, and audit checks into the same governance workflow you use for other machine identities.

Breaches seen in the wild

• Cisco DevHub NHI breach — IntelBroker exploited exposed Cisco credentials, API tokens and keys in DevHub.
• Azure Key Vault privilege escalation exposure — Azure Key Vault Contributor role misconfiguration enabled privilege escalation.

Read our 52 NHI Breaches Analysis report for a comprehensive view of breaches impacting Non-Human Identities including AI Agents.

NHI Mgmt Group analysis

SSH keys are an NHI governance problem first and a cryptography problem second. The article correctly explains the mechanics of public-private key authentication, but the real risk sits in unmanaged credential lifecycle. Once an SSH key is embedded in a workflow, copied between systems, or never removed after a role change, it becomes a standing access path. Practitioners should treat SSH keys as governed machine identities, not static configuration artefacts.

Key algorithm choice does not compensate for access sprawl. RSA, DSA, and ECDSA matter for cryptographic properties, but none of them solve the operational failure mode of persistent credentials spread across hosts. The decision point for security leaders is whether the programme can inventory where keys exist, who owns them, and when they are meant to disappear. That is the control boundary that matters under OWASP-NHI and NIST-CSF.

SSH lifecycle governance is the part most teams underbuild. The article highlights onboarding and offboarding as pain points, which is where access control becomes real. If keys are distributed manually and revocation is delayed, the organisation has created an identity residue problem. Practitioners should map SSH access to joiner-mover-leaver processes and audit it like any other privileged NHI.

Centralised control is only effective when it is paired with accountability. Visibility into key use, ownership, and change history is what allows administrators to distinguish an active operational credential from an orphaned one. Without that linkage, monitoring becomes inventory theatre. The practical conclusion is simple: govern SSH keys with the same discipline used for service accounts and other persistent non-human identities.

SSH access should be treated as part of zero trust, not an exception to it. A passwordless flow is not automatically a trustless flow. If the server accepts an old key indefinitely, the access path remains valid long after the human context has changed. That is why strong authentication must be matched with revocation, review, and least-privilege enforcement across the full SSH lifecycle.

From our research:

• Only 20% have formal processes for offboarding and revoking API keys, and even fewer have procedures for rotating them, according to Ultimate Guide to NHIs.
• 91.6% of secrets remain valid five days after the targeted organisation is notified, showing a critical gap in remediation procedures.
• That gap is why Ultimate Guide to NHIs , Key Challenges and Risks is the right next step for teams trying to reduce credential persistence.

What this signals

Credential persistence is the hidden risk in SSH estates. Even when teams standardise on stronger algorithms, the operational problem remains unchanged if keys are not inventoried, rotated, and removed at the end of the trust relationship. That is the core reason SSH should be managed through NHI lifecycle controls, not left inside ad hoc server administration.

With 96% of organisations storing secrets outside secrets managers in vulnerable locations including code, config files, and CI/CD tools, per the Ultimate Guide to NHIs, the same pattern can easily appear in SSH key handling. If your programme does not know where every key lives, it does not control the access path.

Identity residue: SSH access that remains valid after role change or system decommission is a governance failure, not a cryptographic failure. Teams should watch for keys that continue to work after offboarding, because that signal shows the access model is outliving accountability.

For practitioners

• Inventory every SSH key pair Build a complete record of where keys exist, who owns them, which hosts trust them, and whether they are tied to automation or a named operator. Use that inventory to identify orphaned keys and shared credentials.
• Rotate SSH credentials on a defined cadence Set a rotation policy for long-lived SSH keys and align it with role change, system change, and offboarding events. Avoid leaving keys in place simply because they still work.
• Remove manual key sprawl from server access Move distribution and revocation into a central control point so authorized_keys files are not managed ad hoc across environments. Pair that control with logging so changes are traceable.
• Tie SSH offboarding to lifecycle events Trigger revocation when a user, contractor, or automation path no longer needs access. Offboarding should remove the key from every approved trust location, not just disable one account record.
• Review SSH access as a privileged NHI path Include SSH credentials in privileged access reviews, because they can bypass password controls and persist longer than expected. Treat each key as an elevated credential with its own approval and recertification record.

Key takeaways

• SSH key security depends on lifecycle governance as much as on cryptography, because an unrevoked key remains a live access path.
• The main risk is not RSA versus ECDSA, but unmanaged distribution, weak ownership, and delayed revocation across many systems.
• IAM and PAM teams should treat SSH credentials as privileged NHI assets and subject them to inventory, rotation, and offboarding controls.

Key terms

• SSH Key Pair: A matched public and private key used to authenticate a connection without a password. In practice, the pair is a non-human identity credential, so the governance burden is ownership, storage, rotation, and revocation rather than just algorithm strength.
• Authorized Keys: The server-side list of public keys allowed to authenticate to a user or system account. It is a trust registry, and if it is not reviewed and cleaned up, access can continue long after the original need has ended.
• Key Rotation: The process of replacing a credential with a fresh one before the old credential becomes too risky or stale. For SSH, rotation only reduces risk when the old key is actually removed everywhere it was trusted, not just reissued elsewhere.
• Privileged Non-Human Identity: A non-human credential that can reach production systems, infrastructure, or sensitive data paths. SSH keys often fall into this category because they can grant elevated administrative access, which means they belong inside PAM and lifecycle governance workflows.

Deepen your knowledge

SSH key lifecycle governance is a core topic in our NHI Foundation Level course, the industry's only accredited NHI security programme. If you are building control over server access and privileged machine credentials, it is worth exploring.

This post draws on content published by StrongDM: Comparing SSH Keys: A Comprehensive Guide (RSA, DSA, ECDSA). Read the original.