[erlang-questions] rsa encryption/decryption example code doesn't work

[Chad DePue]

I have written this sample rsa encryption code and it doesn't decrypt
properly. I generated the test private key using ssh-keygen. any
ideas? thanks in advance...

chad

-module(crypttest).
-include_lib("public_key/include/public_key.hrl").
-export([testcase/0]).

testcase() ->
{ok,[Entry]} = public_key:pem_to_der("./test_private_key"),
{ok,{'RSAPrivateKey', 'two-prime', N , E, D, _P, _Q, _E1, _E2, _C,
_Other}} = public_key:decode_private_key(Entry),
PrivKey = [crypto:mpint(E), crypto:mpint(N), crypto:mpint(D)] ,
Foo = crypto:rsa_private_encrypt("now is the time for all good men
to come to the aid of their country",PrivKey,rsa_pkcs1_padding),
Bar = crypto:rsa_private_decrypt(Foo,PrivKey,rsa_pkcs1_padding),
Foo == Bar.

8> c(crypttest).
{ok,crypttest}
9> crypttest:testcase().

** exception error: decrypt_failed
in function crypto:rsa_private_decrypt/3
called as
crypto:rsa_private_decrypt
(<<141,9,170,241,244,57,128,44,178,223,162,109,80,60,225,

19,84,133,118,45,2,19,36,111,58,236,38,98,...>>,
[<<0,0,0,1,35>>,

<<0,0,1,1,0,162,240,42,103,51,152,51,159,139,165,248,162,

95,223,62,6,52,130,119,213,...>>,

<<0,0,1,1,0,158,72,99,180,181,199,13,147,172,58,212,69,

246,187,155,86,124,38,248,...>>],
rsa_pkcs1_padding)
in call from crypttest:testcase/0

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[Richard Andrews]

On Sun, Jun 28, 2009 at 7:52 AM, Chad DePue<ch...@inakanetworks.com> wrote:
> I have written this sample rsa encryption code and it doesn't decrypt
> properly.  I generated the test private key using ssh-keygen. any ideas?
> thanks in advance...
>
> chad
>
>
> -module(crypttest).
> -include_lib("public_key/include/public_key.hrl").
> -export([testcase/0]).
>
> testcase() ->
>  {ok,[Entry]} = public_key:pem_to_der("./test_private_key"),
>  {ok,{'RSAPrivateKey', 'two-prime', N , E, D, _P, _Q, _E1, _E2, _C, _Other}}
> =  public_key:decode_private_key(Entry),
>  PrivKey = [crypto:mpint(E), crypto:mpint(N), crypto:mpint(D)] ,
>  Foo = crypto:rsa_private_encrypt("now is the time for all good men to come
> to the aid of their country",PrivKey,rsa_pkcs1_padding),
>  Bar = crypto:rsa_private_decrypt(Foo,PrivKey,rsa_pkcs1_padding),
>  Foo == Bar.

For asymmetric encryption, one generally encrypts with one key and
decrypts with the other. In this case you are encrypting with PrivKey
so you will need to decrypt with PubKey.

--
Rich

[Chad DePue]

Thanks, Rich - that did it. Here's the final code.

-module(crypttest).
-include_lib("public_key/include/public_key.hrl").
-export([testcase/0]).

testcase() ->
{ok,[Entry]} = public_key:pem_to_der("./test_private_key"),
{ok,{'RSAPrivateKey', 'two-prime', N , E, D, _P, _Q, _E1, _E2, _C,
_Other}} = public_key:decode_private_key(Entry),

PlainText = "now is the time for all good men to come to the aid of
their country",

PrivKey = [crypto:mpint(E), crypto:mpint(N), crypto:mpint(D)] ,

PubKey = [crypto:mpint(E), crypto:mpint(N)],
Foo =
crypto:rsa_private_encrypt(PlainText,PrivKey,rsa_pkcs1_padding),
Bar = crypto:rsa_public_decrypt(Foo,PubKey,rsa_pkcs1_padding),
PlainText == binary_to_list(Bar).

7> c(crypttest).
{ok,crypttest}
8> crypttest:testcase().
true