hash_sha1

This page explains how to use the hash_sha1 function in APL.

Introduction

The hash_sha1 function returns the SHA-1 hash of a scalar value as a 40-character hexadecimal string. Use it to generate consistent identifiers, detect duplicates across datasets, or fingerprint values for comparison.

SHA-1 produces a 160-bit digest that's faster to compute than SHA-256 while producing a larger output than MD5. SHA-1 is deprecated for cryptographic security use cases, but remains appropriate for non-security tasks such as data deduplication, fingerprinting, and consistent grouping. For security-sensitive hashing, use hash_sha256 or hash_sha512.

Usage

Syntax

hash_sha1(source)

Parameters

Name	Type	Required	Description
source	scalar	Yes	The value to hash. APL converts it to a string before hashing.

Returns

The SHA-1 hash of source as a 40-character lowercase hexadecimal string.

Use case examples

Anonymize user IDs and count requests per hashed user to protect PII while tracking usage patterns.

Query

['sample-http-logs']
| extend hashed_id = hash_sha1(id)
| summarize request_count = count() by hashed_id
| top 5 by request_count

Run in Playground

Output

hashed_id	request_count
9f9af029585ba014e07cd3910ca976cf56160616	128
a94a8fe5ccb19ba61c4c0873d391e987982fbbd3	97
356a192b7913b04c54574d18c28d46e6395428ab	85
da4b9237bacccdf19c0760cab7aec4a8359010b0	74
77de68daecd823babbb58edb1c8e14d7106e83bb	69

The query replaces raw user IDs with SHA-1 hashes before aggregating, so the busiest users are visible without exposing their original identifiers.

Hash span IDs to create stable surrogate keys for cross-dataset joins or external reporting.

Query

['otel-demo-traces']
| extend hashed_span = hash_sha1(span_id)
| project _time, ['service.name'], hashed_span, duration
| take 10

Run in Playground

Output

_time	service.name	hashed_span	duration
2024-01-15 10:23:01	frontend	9f9af029585ba014e07cd3910ca976cf56160616	320ms
2024-01-15 10:23:02	checkout	a94a8fe5ccb19ba61c4c0873d391e987982fbbd3	875ms
2024-01-15 10:23:03	cart	356a192b7913b04c54574d18c28d46e6395428ab	140ms

The query projects the hashed span ID alongside service name and duration so you can work with span fingerprints in downstream pipelines.

hash_md5: Returns a 32-character MD5 hex digest. Use hash_md5 when a shorter digest is sufficient and speed is the priority.
hash_sha256: Returns a 64-character SHA-256 hex digest. Use hash_sha256 for security-sensitive hashing.
hash_sha512: Returns a 128-character SHA-512 hex digest for maximum hash strength.
hash: Returns a signed 64-bit integer hash. Use hash when you need a compact numeric key rather than a hex string.