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This function uses the private key handle to sign the
data. To verify the signature use xp_rsa_verify.
XP_CRYPT makes RSA-MD5 signature. For this operation the keys that are
longer than 512 bytes are required. If you use the demo version of
XP_CRYPT you cannot generate
keys longer than 256 bits. The free version contains 2 pregenerated keys:
publickey512.pem and privatekey512.pem. You can use them for testing. The
password for the private key is xp_crypt.
Syntax
xp_rsa_sign { variable1 [, variable2 , variable3 ...] ,
private_key_src, signature OUTPUT, [src_password]}
Arguments
variable1 [, variable2 , variable3 ...]
One or more variables to sign. The order of the variables is important.
If you put the same variables in another order the digital sign will be
completely different.
private_key_src
VARCHAR. Source of the private key. It can be a handle, a filename or a key body.
signature
VARCHAR or VARBINARY. A unique signature value for this set of variables. The output
length of this variable does not depend on the amount of data you sign, but only
on the size of the key you use.
src_password
VARCHAR. Password for reading the key if its source is in the file of key
string. If the pswd_cache option is set to yes and the given
password is '?' XP_CRYPT will try to load the key with the password
stored in the session. See xp_crypt_set_option
for more information about pswd_cache option.
Permissions
Execute permissions default to the public role.
Return Code Values
0 - success, or Error code
if failed. Signature IS NOT NULL (success) or IS NULL (failure)
Example
-- String signung with key stored in .pem file. Key will be
loaded and freed automatically
exec xp_rsa_sign 'Show must go on' , '<pubkey.pem' , @sign
OUTPUT
-- Shows new bulk encryption feature
declare @name as varchar (100)
declare @dateofbirth as datetime
declare @department int
declare @sign VARCHAR(8000)
select @name=name_field , @dateofbirth=dateofbirth_field ,
@department = department_field from employees
exec xp_rsa_sign @name, @dateofbirth , @department , '<privatekey.pem' ,
@sign output, 'MyPassword'
-- @sign contains the base64 encoded sign of 3 fields joined together. If you modify any of those fields xp_rsa_verify will
fail
-- Let's check the signature
exec xp_rsa_verify @name, @dateofbirth , @department , '<publickey.pem',
@sign , @result OUTPUT
if @result is not null and @result = 1
begin
-- Exactly this variables was signed by our private key!
...
else
-- Someone has modificated our data ! Probably it is not valid !
...
end
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