⨳ a function to mask strings ⨳

July 21, 2020

here’s a handy function to mask strings while retaining some useful metadata. this is helpful in identifying patterns in identifiers.

CREATE TEMPORARY FUNCTION mask_string(str STRING, n INT64) AS (
  -- keep first n characters of a string, mask remaining characters
  CASE
    WHEN REGEXP_CONTAINS(TRIM(str), r'^[0-9-]{8,}$') -- only digits
    THEN CONCAT(TRIM(SUBSTR(str, 1, n)), REGEXP_REPLACE(TRIM(SUBSTR(str,n+1)),r'[0-9]', '#'))
    WHEN REGEXP_CONTAINS(TRIM(str), r'^[a-zA-Z-]{8,}$') -- only letters
    THEN CONCAT(TRIM(SUBSTR(str, 1, n)),REGEXP_REPLACE(TRIM(SUBSTR(str,n+1)),r'[a-zA-Z]', '@'))
    WHEN REGEXP_CONTAINS(TRIM(str), r'^[a-fA-F0-9-]{8,}$') -- hex-like strings
    THEN CONCAT(TRIM(SUBSTR(str, 1, n)),REGEXP_REPLACE(TRIM(SUBSTR(str,n+1)),r'[a-fA-F0-9]', '⨳'))
    ELSE CONCAT(TRIM(SUBSTR(str, 1, n)),REGEXP_REPLACE(TRIM(SUBSTR(str,n+1)),r'.', '*'))
  END
);

We can see this in action by generating some fake identifiers.

SELECT NUMERIC_ID , mask_string(NUMERIC_ID, 1) AS masked_NUMBERID_ID_1,
  HEX_ID, mask_string(HEX_ID, 0) AS masked_HEX_ID_0, mask_string(HEX_ID, 2) AS masked_HEX_ID_2,
  MESSY_ID , mask_string(MESSY_ID, 1) AS masked_MESSY_ID_1
FROM ( -- fake some data
  SELECT
    SUBSTR(FORMAT("%17.15f", RAND()), 3) AS NUMERIC_ID ,
    SUBSTR(GENERATE_UUID(), 15) AS HEX_ID ,
    TO_BASE64(SUBSTR(SHA256(FORMAT("%17.15f", RAND())), 15)) AS MESSY_ID
  FROM ( -- get 10 records
    SELECT x FROM UNNEST(GENERATE_ARRAY(1,10)) x
  )
)
;

And the results. Notice the 5th result for MESSY_ID is all-letters, so it unfortunately gets the all-letter treatment.

NUMERIC_ID masked_NUMBERID_ID_1 HEX_ID masked_HEX_ID_0 masked_HEX_ID_2 MESSY_ID masked_MESSY_ID_1
321955549450509 3############## 429c-970a-066bfdc17fa4 ⨳⨳⨳⨳-⨳⨳⨳⨳-⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳ 42⨳⨳-⨳⨳⨳⨳-⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳ ihF5HMlhwbTR4I1GzBYyXpuZ i***********
092285814003594 0############## 4364-89ea-148cd4891a9f ⨳⨳⨳⨳-⨳⨳⨳⨳-⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳ 43⨳⨳-⨳⨳⨳⨳-⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳ qqCJAV2tyEx/Rl/gqutED5A8 q***********
721307759069463 7############## 4780-bca6-ee3999c7a391 ⨳⨳⨳⨳-⨳⨳⨳⨳-⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳ 47⨳⨳-⨳⨳⨳⨳-⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳ 7QEo+6y/wxMxwhtU1NoFcUVL 7***********
195911564152664 1############## 4d55-b870-3433e43100b8 ⨳⨳⨳⨳-⨳⨳⨳⨳-⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳ 4d⨳⨳-⨳⨳⨳⨳-⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳ EoQTEkXSwD+ElwZ5pq7h+vSo E***********
395125327917730 3############## 4e11-b5af-7d83b2247273 ⨳⨳⨳⨳-⨳⨳⨳⨳-⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳ 4e⨳⨳-⨳⨳⨳⨳-⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳ ydnPKSZIkFCDeSYGJIabZwRo y@@@@@@@@@@@@@@@@@@@@@@@
240142410689042 2############## 4ea0-9e0b-dc8a2b818605 ⨳⨳⨳⨳-⨳⨳⨳⨳-⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳ 4e⨳⨳-⨳⨳⨳⨳-⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳ 9exU7igSR1MmyRkHHGy1Tkap 9***********
924742093246825 9############## 4a27-b440-629f23283b94 ⨳⨳⨳⨳-⨳⨳⨳⨳-⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳ 4a⨳⨳-⨳⨳⨳⨳-⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳ WmfYNaFow4xiUmPPqiA/5/mB W***********
208147183726515 2############## 4cfc-8d05-c43cb9a720fd ⨳⨳⨳⨳-⨳⨳⨳⨳-⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳ 4c⨳⨳-⨳⨳⨳⨳-⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳ KMeTzPpJmR6ZZbqtX1r8s1JK K***********
138648685501020 1############## 4b45-baf4-2602996a523a ⨳⨳⨳⨳-⨳⨳⨳⨳-⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳ 4b⨳⨳-⨳⨳⨳⨳-⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳ Z8DV26m9QAOY/cWs6L5QDpOu Z***********
618787412556747 6############## 439c-b218-6ba5d73e7c48 ⨳⨳⨳⨳-⨳⨳⨳⨳-⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳ 43⨳⨳-⨳⨳⨳⨳-⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳ fCiXlZDCzM7suA1xKZS6515x f***********

Extending this a bit to provide some view of aggregations:

SELECT mask_string(NUMERIC_ID, 1) AS PATTERN , COUNT(1) AS N
FROM (
  SELECT
    SUBSTR(FORMAT("%17.15f", RAND()), 3) AS NUMERIC_ID ,
    SUBSTR(GENERATE_UUID(), 15) AS HEX_ID ,
    TO_BASE64(SUBSTR(SHA256(FORMAT("%17.15f", RAND())), 15)) AS MESSY_ID
  FROM (
    SELECT x FROM UNNEST(GENERATE_ARRAY(1,100000)) x
  )
)
GROUP BY 1
ORDER BY 1
;
PATTERN N
0############## 9949
1############## 10005
2############## 9999
3############## 10020
4############## 10087
5############## 10003
6############## 9996
7############## 10053
8############## 10050
9############## 9838

Masking all but the first 2 characters of MESSY_ID yields a 4,697-long table:

PATTERN N
++******** 30
+/******** 26
+0******** 32
+1******** 18
+2******** 28

This type of aggregation is useful when comparing overlapping and non-overlapping identifiers across disparate data sources to help narrow down what a “good” identifier looks like vs. the noise. For example:

ID_LENGTH ID_PATTERN IN_DATA1_CNT IN_DATA1_PCT IN_BOTH_CNT IN_DATA2_PCT IN_DATA2_CNT
8 ######## 321547 0.9814117376308906 315570 0.8179859975271456 385789
4 ** 202 0.6683168316831684 135 0.051350323316850514 2629
5 ***** 1935 0.6217054263565891 1203 0.04688230709275137 25660
6 ** 19923 0.635546855393264 12662 0.048300959763187205 262148
7 *** 158119 0.5859574118227411 92651 0.04273678529667496 2167945
8 ######## 4965619 0.262163488580175 1301804 0.09105307969763868 14297199
9 ######### 55422 0.33896286673162285 18786 0.048430756856254545 387894
64 ⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳⨳ 495494 0.25489713296225586 126300 0.09994579345327356 1263685

a function to mask strings - July 21, 2020 -