Evidence Integrity Calculator
Time a SHA-256 verification pass over an evidence set and check the hash algorithm still offers real collision resistance.
About Evidence Integrity Calculator
Hashing is embarrassingly parallel across separate images, so throughput scales with streams until the storage read rate saturates — which on anything other than local NVMe is usually the real limit. Collision resistance is half the digest length because of the birthday bound, which is why SHA-1's 80 bits is no longer defensible. The verification hash is what makes evidence admissible, and knowing that a full pass over four terabytes takes about an hour rather than a day is what stops verification being quietly skipped under deadline pressure.
Formulas
Evidence Integrity
Verification time = evidence bytes ÷ min(per-core throughput × streams, storage read ceiling), and total time multiplies by the number of passes.
- per-core throughput
- ≈500 MB/s with SHA-NI, ≈150 MB/s without
- streams
- Parallel hashing streams across images
- read ceiling
- Sustained read rate of the evidence storage
Collision resistance
Collision resistance = digest length ÷ 2 bits, by the birthday bound — 128 bits for SHA-256.
- digest length
- Hash output size in bits
- ÷ 2
- Birthday bound on collision search
Worked example
With the default values below, Evidence Integrity Calculator returns Time for One Verification Pass of 0.93. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Evidence to verifyaccepts 0.001–10,000 TB
- 4 TB
- Hash algorithmone of SHA-256 — 256-bit digest, SHA-512 — 512-bit digest, SHA-1 — 160-bit, deprecated, MD5 — 128-bit, broken
- SHA-256 — 256-bit digest
- Hash throughput per coreaccepts 1–10,000 MB/s
- 500 MB/s
- Parallel hashing streamsaccepts 1–256 streams
- 4 streams
- Storage read ceilingaccepts 1–100,000 MB/s
- 1,200 MB/s
- Verification passesaccepts 1–10 passes
- 2 passes
- Images in the evidence setaccepts 1–100,000 images
- 25 images
Results
- Time for One Verification Pass
- 0.93 hours
- Effective Throughput
- 1,200 MB/s
- Time for All Passes
- 1.85 hours
- Minutes per Image
- 2.2 minutes
- Collision Resistance
- 128 bits
- Limiting Factor
- Storage read speed — hashing capacity of 2000 MB/s is idle waiting on I/O
- Algorithm Verdict
- Sound — 128-bit collision resistance is beyond any practical attack
Step by step
- 1Values used
- 2Evidence Integrity
- 3Collision resistance
- 4Time for One Verification Pass= 0.93 hours
- 5Effective Throughput= 1,200 MB/s
- 6Time for All Passes= 1.85 hours
- 7Minutes per Image= 2.2 minutes
- 8Collision Resistance= 128 bits
- 9Limiting Factor= Storage read speed — hashing capacity of 2000 MB/s is idle waiting on I/O
Assumptions and limits
- The result is derived only from the 7 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 2 decimal places, 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 Evidence Integrity calculated?
Verification time = evidence bytes ÷ min(per-core throughput × streams, storage read ceiling), and total time multiplies by the number of passes. Hashing is embarrassingly parallel across separate images, so throughput scales with streams until the storage read rate saturates — which on anything other than local NVMe is usually the real limit. Collision resistance is half the digest length because of the birthday bound, which is why SHA-1's 80 bits is no longer defensible.
Why does Evidence Integrity matter?
The verification hash is what makes evidence admissible, and knowing that a full pass over four terabytes takes about an hour rather than a day is what stops verification being quietly skipped under deadline pressure.
What values do I need to enter?
This calculator takes 7 inputs: Evidence to verify, Hash algorithm, Hash throughput per core, Parallel hashing streams, Storage read ceiling, Verification passes, Images in the evidence set. 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 SHA-1 still acceptable for evidence?
No. Practical chosen-prefix collisions against SHA-1 have been demonstrated at modest cost, so an opposing expert can credibly challenge it. Use SHA-256, and if you must keep legacy SHA-1 values for continuity, record both.
Why hash more than once?
Each pass proves integrity at a different point in the custody chain: at acquisition to fix the baseline, before analysis to prove the working copy matches, and before disclosure to prove nothing changed while in your care. Each pass is a separate, timestamped custody record.