[erlang-questions] blowfish cbc mode decrypt

Bogdan Andu <>
Mon Nov 9 14:17:56 CET 2015


I have DataToBeDecrypted

and one-liner in erlang shell:

crypto:block_decrypt(blowfish_cbc, hexstr2bin(Key), IV, Rest).

where DataToBeDecrypted is formatted as follows:

<<IvSpec:8/binary, IV:8/binary, Rest/binary>> = DataToBeDecrypted

I can extract IvSpec = <<"RandomIV">>,

Next 8 octets is IV,

Rest should bet the actual quantity to be decrypted,

and the function call above fails to produce the plain text expected,
only garbage

Unfortunately Key is sensitive and cannot disclose the value.

On Mon, Nov 9, 2015 at 11:40 AM, Rad Gruchalski <>
wrote:

> Bogdan,
>
> I wonder if you can show us a minimum viable example.
> How do you encrypt, how do you decrypt. Can you present such code?
>
> Kind regards,
> Radek Gruchalski
>  <>
> de.linkedin.com/in/radgruchalski/
>
>
> *Confidentiality:*This communication is intended for the above-named
> person and may be confidential and/or legally privileged.
> If it has come to you in error you must take no action based on it, nor
> must you copy or show it to anyone; please delete/destroy and inform the
> sender immediately.
>
> On Monday, 9 November 2015 at 10:38, Bogdan Andu wrote:
>
>
> hi,
>
> I really need some pointers about this issue
>
> as i tried all kinds of combinations of IV and body
> to be decrypted.
>
> Am i missing something or there is a bug in cipher
> blowfish_cbc ?
>
>
>
> On Thu, Nov 5, 2015 at 3:51 PM, Bogdan Andu <> wrote:
>
>  Data to be decrypted (arrived on socket, etc) is:
> <<IvSpec:8/binary, IV:8/binary, Rest/binary>> = EncryptedData
>
> IV is ectracted form the 8-byte prepanded value preceding
> IvSpec which has the value RandomIV.
>
> decryption of Rest should be initialized with IV.
>
>
> On Thu, Nov 5, 2015 at 3:38 PM, Radoslaw Gruchalski <>
> wrote:
>
> You say your data is:
>
> <<IvSpec>> == <<RandomIv>>
>
> But you read:
>
> Is your data <<IvSpec:8/binary, IV:8/binary, Rest/binary>>
>
> Should it not be just:
>
> <<IV:8/binary, Rest/binary>>
>
> ?
>
> Sent from Outlook <http://aka.ms/Ox5hz3>
>
> _____________________________
> From: Bogdan Andu <>
> Sent: Thursday, November 5, 2015 2:26 p.m.
> Subject: [erlang-questions] blowfish cbc mode decrypt
> To: Erlang <>
>
>
>
> Hi,
>
> I have a stream of data called EncryptedData (with randomiv header
> specification).
> I want to decrypt  using:
> crypto:block_decrypt(blowfish_cbc, hexstr2bin(Key), IV, Rest).
>
> where:
>
> EncryptedData is formatted as follows:
> <<IvSpec:8/binary, IV:8/binary, Rest/binary>>
>
> IvSpec == <<"RandomIV">>
>
> However the decryption does not works and garbage is generated
> (the function  ) .
>
> What could be done given the fact that IV is an 8-byte quantity
> the Key is formatted according to crypto test suites and is 16 bytes long
>
> Am I missing something?
>
> Thanks,
>
> Bogdan
>
>
>
>
>
>
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