SQL Server

Example: Hash Text in Chunks

Shows how to generate a final hash, like SHA-256, for a large text by processing it in chunks. SQL Server

-- Important: See this note about string length limitations for strings returned by sp_OAMethod calls.
--
CREATE PROCEDURE ChilkatSample
AS
BEGIN
    DECLARE @hr int
    DECLARE @success int
    SELECT @success = 0

    DECLARE @crypt int
    EXEC @hr = sp_OACreate 'Chilkat.Crypt2', @crypt OUT
    IF @hr <> 0
    BEGIN
        PRINT 'Failed to create ActiveX component'
        RETURN
    END

    EXEC sp_OASetProperty @crypt, 'HashAlgorithm', 'sha256'
    EXEC sp_OASetProperty @crypt, 'Charset', 'utf-8'

    DECLARE @bd int
    EXEC @hr = sp_OACreate 'Chilkat.BinData', @bd OUT

    DECLARE @s nvarchar(4000)
    SELECT @s = 'The quick brown fox jumped over the lazy dog.' + CHAR(13) + CHAR(10)

    -- Accumulate the text in a StringBuilder.  We'll demonstrate hashing the text in chunks,
    -- and then also hashing the entire text at once to show the results are the same.

    EXEC sp_OAMethod @bd, 'AppendString', @success OUT, @s, 'utf-8'
    EXEC sp_OAMethod @crypt, 'HashBeginString', @success OUT, @s

    DECLARE @i int
    SELECT @i = 0
    WHILE @i < 200
      BEGIN
        EXEC sp_OAMethod @bd, 'AppendString', @success OUT, @s, 'utf-8'
        EXEC sp_OAMethod @crypt, 'HashMoreString', @success OUT, @s
        SELECT @i = @i + 1
      END

    -- Get the hash in base64 format.
    EXEC sp_OASetProperty @crypt, 'EncodingMode', 'base64'

    DECLARE @encodedHash nvarchar(4000)
    EXEC sp_OAMethod @crypt, 'HashFinalENC', @encodedHash OUT

    PRINT 'Hash computed in chunks: ' + @encodedHash

    -- Let's alternatively compute the hash of the entire amount of data at once,
    -- to show the hash computation is the same:
    EXEC sp_OAMethod @crypt, 'HashBdENC', @encodedHash OUT, @bd

    PRINT 'Hash computed in 1 step: ' + @encodedHash

    -- Output:

    -- Hash computed in chunks: unwkVff61k40roRIJizaknreScHaL6frWe37kydXbZQ=
    -- Hash computed in 1 step: unwkVff61k40roRIJizaknreScHaL6frWe37kydXbZQ=

    EXEC @hr = sp_OADestroy @crypt
    EXEC @hr = sp_OADestroy @bd


END
GO