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API Authentication Strength Calculator

Score API authentication on mechanism, credential entropy, rotation, replay protection, secret storage, MFA and lockout.

About API Authentication Strength Calculator

The mechanism carries the largest weight because it decides what an attacker needs to steal: a private key that never leaves the client, a short-lived token, or a static string that works forever. Entropy, rotation and storage then determine how likely that credential is to leak and how long a leak stays useful. Most API breaches are not exploits but credentials — a key committed to a repository, a token in a log, a shared secret that has not rotated since the integration went live.

Formula

API Authentication Strength

Authentication score = mechanism (28 mTLS … 0 none) + entropy score (10 at ≥256 bits … 0 below 32) + rotation score (10 at ≤30 days … 0 above a year) + 12 replay protection + 12 secret storage + 10 scoping + 10 MFA on issuance + 8 lockout = 100.

mechanism
How the caller proves identity
entropy score
Credential length in bits, scored
rotation score
How often credentials are replaced

Worked example

With the default values below, API Authentication Strength Calculator returns Authentication Score of 71. Change any input above and every figure here is recalculated in your browser.

Inputs used

Authentication mechanismone of Mutual TLS with certificate pinning — 28, OAuth 2.0 client credentials with short-lived JWTs — 26, HMAC-signed requests — 22, Bearer API key — 12, HTTP Basic — 6, None or a shared secret in the URL — 0
HMAC-signed requests — 22
Credential entropyaccepts 16–512 bits
128 bits
Nonce and timestamp replay protection
No
Credential rotation intervalaccepts 1–3,650 days
90 days
Least-privilege scopes per credential
Yes
Secrets held in a KMS or vault, never in source
Yes
MFA on the human path that issues credentials
Yes
Failed-attempt throttling or lockout
No

Results

Authentication Score
71 / 100
Authentication Grade
C — Fair
Credential Entropy
Strong — guessing is not a practical path
Weakest Link
Replay protection — add a signed nonce and timestamp
Residual Exposure
29%
Replay Exposure
Exposed — any captured request can be replayed verbatim

Step by step

  1. 1Values used
  2. 2API Authentication Strength
  3. 3Authentication Score= 71 / 100
  4. 4Authentication Grade= C — Fair
  5. 5Credential Entropy= Strong — guessing is not a practical path
  6. 6Weakest Link= Replay protection — add a signed nonce and timestamp
  7. 7Residual Exposure= 29
  8. 8Replay Exposure= Exposed — any captured request can be replayed verbatim

Assumptions and limits

  • The result is derived only from the 8 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to whole numbers, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is API Authentication Strength calculated?

Authentication score = mechanism (28 mTLS … 0 none) + entropy score (10 at ≥256 bits … 0 below 32) + rotation score (10 at ≤30 days … 0 above a year) + 12 replay protection + 12 secret storage + 10 scoping + 10 MFA on issuance + 8 lockout = 100. The mechanism carries the largest weight because it decides what an attacker needs to steal: a private key that never leaves the client, a short-lived token, or a static string that works forever. Entropy, rotation and storage then determine how likely that credential is to leak and how long a leak stays useful.

Why does API Authentication Strength matter?

Most API breaches are not exploits but credentials — a key committed to a repository, a token in a log, a shared secret that has not rotated since the integration went live.

What values do I need to enter?

This calculator takes 8 inputs: Authentication mechanism, Credential entropy, Nonce and timestamp replay protection, Credential rotation interval, Least-privilege scopes per credential, Secrets held in a KMS or vault, never in source, MFA on the human path that issues credentials, Failed-attempt throttling or lockout. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.

Is HMAC request signing better than a bearer token?

For server-to-server calls, usually yes. The signing key never travels, so a captured request cannot be replayed against another endpoint, and adding a nonce and timestamp to the signed payload blocks replay entirely. Bearer tokens are simpler and fine when they are short-lived and sent only over TLS.

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