CRYPT_GEN_RANDOM (Transact-SQL)
Applies to: 
SQL Server
Azure SQL Database
Azure SQL Managed Instance
This function returns a cryptographic, randomly-generated number, generated by the Crypto API (CAPI). CRYPT_GEN_RANDOM returns a hexadecimal number with a length of a specified number of bytes.
Transact-SQL syntax conventions
Syntax
CRYPT_GEN_RANDOM ( length [ , seed ] )
Arguments
length
The length, in bytes, of the number that CRYPT_GEN_RANDOM will create. The length argument has an int data type, and a value range between 1 and 8000. CRYPT_GEN_RANDOM returns NULL for an int value outside this range.
seed
An optional hexadecimal number, for use as a random seed value. The length of seed must match the value of the length argument. The seed argument has a varbinary(8000) data type.
Returned Types
varbinary(8000)
Permissions
This function is public and it does not require any special permissions.
Examples
A. Generating a random number
This example generates a random number of length 50 bytes:
SELECT CRYPT_GEN_RANDOM(50) ;
This example generates a random number of length 4 bytes, using a 4-byte seed:
SELECT CRYPT_GEN_RANDOM(4, 0x25F18060) ;