On Tue, Sep 21, 2010, Stephan Mller wrote:
> Hello,
>
> I try to understand the encryption of a private rsa key. It was generated
> with
>
> > openssl genpkey -aes-256-cbc -algorithm rsa -out mykey.enc
> -pkeyopt rsa_keygen_bits:2048
>
> (pw: 'admin', file attached)
>
> according to pkcs#8 the result is
>
> EncryptedPrivateKeyInfo ::= SEQUENCE {
> encryptionAlgorithm AlgorithmIdentifier {{KeyEncryptionAlgorithms}},
> encryptedData EncryptedData
> }
>
> parsing through 'encryptionAlgorithm' i got
>
> > openssl asn1parse - in mykey.enc -strparse 4
> 0: d=0 hl=2 l=73 cons : SEQUENCE
> 2: d=1 hl=2 l=9 prim : OBJECT: PBES2
> 13: d=1 hl=2 l=60 cons : SEQUENCE
> 15: d=2 hl=2 l=27 cons : SEQUENCE
> 17: d=3 hl=2 l=9 prim :OBJECT: PBKDF2
> 28: d=3 hl=2 l=14 cons :SEQUENCE
> 30: d=4 hl=2 l=8 prim :OCTET STRING
> [ HEX DUMP ]:7C4B1587B12A7705
> 40: d=4 hl=2 l=2 prim :INTEGER: 0800
> 44: d=2 hl=2 l= 29 cons :SEQUENCE
> 46: d=3 hl=2 l=9 prim :OBJECT :aes-256-cbc
> 57: d=3 hl=2 l=16 prim :OCTET STRING
> [ HEX DUMP ]: 4850BA5F76BA9CD5574F0121D8C0C657.
>
> as i understood the rare documenation, offset 30 is the salt for PBKDF2
> and offset 57 is the IV for aes.
>
> as result of PKCS5_PBKDF2_HMAC_SHA1 fed with the salt from above,
> pw:'admin' and ic:2048 (offset 40 above) i got:
>
> K = dc55f54889fe64153fb1b181e89ec5c08a864ef5f777d6aa1d0be9ff82dd8b3a
> iv = 11be3aafd0768fd9fdbc7880936ad2c4
>
> decryption with this key (and any of those ivs) fails.
>
> How can i reproduce the data in offset 57? if its really an iv why is it
> written explicitly if it could be calculated a result of PBKDF2?
>
> Does anyone have some hints?
>
The IV is generated randomly and included explicitly. It is done this way
because that's what the PKCS#5 PBES2 standards require. You only generate
keying material using PBKDF2.
If you set the option DEBUG_PKCS5V2 when you compile OpenSSL (or just
uncomment it from p5_crpt2.c in source it will print out the keying material
and parameters used.
Steve.
--
Dr Stephen N. Henson. OpenSSL project core developer.
Commercial tech support now available see: http://www.openssl.org
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