Right, I had missed that algorithm identifier is a sequence. Now it makes
sence. Thanks!
--
R
----------------------------------------
> From: [EMAIL PROTECTED]
> To: openssl-users@openssl.org
> Subject: Re: DER encoding SubjectPublicKeyInfo
> Date: Tue, 22 Apr 2008 14:39:34 +0200
>
> you can see using the lengths the second sequence contains only
> algoritm oid and parameters (in this case NULL parameters). This is
> AlgorithmIdentifier.
> Below the bit string contains the der encoding of subjectPublicKey
> (encoded).
>
>
> Francesco Petruzzi
>
> [EMAIL PROTECTED]
>
>
> ----- Original Message -----
> From: "Roger Boden"
> To:
> Sent: Tuesday, April 22, 2008 11:43 AM
> Subject: RE: DER encoding SubjectPublicKeyInfo
>
>
>
> Thanks, that explains the 0x30 tag value. What about the DER encoding? Is
> that correct?
> The 'openssl asn1parse' output of the DER encoding is:
> 0:d=0 hl=3 l= 159 cons: SEQUENCE
> 3:d=1 hl=2 l= 13 cons: SEQUENCE
> 5:d=2 hl=2 l= 9 prim: OBJECT :rsaEncryption
> 16:d=2 hl=2 l= 0 prim: NULL
> 18:d=1 hl=3 l= 141 prim: BIT STRING
>
> To me this does not look correct. There is a NULL object that should not be
> there. Also the algorithm identifier and the bit string should be in the
> same sequence.
>
> What ASN.1 type is i2d_X509_PUBKEY() supposed to encode? Is this a bug in
> this function, or am I using the wrong API?
>
> Regards Roger
>
> ----------------------------------------
>> To: openssl-users@openssl.org
>> Subject: Re: DER encoding SubjectPublicKeyInfo
>> From: [EMAIL PROTECTED]
>> Date: Tue, 22 Apr 2008 00:09:21 +0200
>>
>> Hello,
>>
>> [EMAIL PROTECTED] wrote on 04/21/2008 10:45:18 PM:
>>
>>>
>>> Hi,
>>>
>>> I need to DER encode an RSA public key as a SubjectPublicKeyInfo. The
>> ASN.1 definition
>>> of SubjectPublicKeyInfo is
>>> SubjectPublicKeyInfo ::= SEQUENCE {
>>> algorithm AlgorithmIdentifier,
>>> subjectPublicKey BIT STRING }
>>>
>>> According to rfc 3279, the bit string subjectPublicKey should hold the
>> DER encoding of
>>> the following ASN.1 defintion:
>>> RSAPublicKey ::= SEQUENCE {
>>> modulus INTEGER, -- n
>>> publicExponent INTEGER } -- e
>>>
>>> In order to achieve this encoding I tried to call i2d_X509_PUBKEY(). The
>> DER output of
>>> this function for an RSA test key is:
>>> 0x30 0x81 0x9f 0x30 0x0d 0x06 0x09 0x2a
>>> 0x86 0x48 0x86 0xf7 0x0d 0x01 0x01 0x01
>>> 0x05 0x00 0x03 0x81 0x8d 0x00 0x30 0x81
>>> 0x89 0x02 0x81 0x81 0x00 0xac 0xaa 0x98
>>> 0xf8 0xeb 0x58 0x8c 0x0d 0xec 0xf3 0xbe
>>> 0xd4 0xd0 0xd0 0xe8 0x0a 0x4d 0x02 0x70
>>> 0x30 0xa1 0x1f 0xea 0xa1 0x02 0xaa 0x9d
>>> 0xb0 0x16 0x91 0x8a 0x39 0xfe 0x79 0x9a
>>> 0xf3 0x46 0xbb 0xc9 0x49 0x23 0x9d 0x37
>>> 0xa5 0x13 0xe6 0x2f 0x9e 0xe3 0x94 0xfb
>>> 0x31 0xd9 0x8d 0x80 0x79 0x7d 0xbe 0xdf
>>> 0x1e 0xf4 0x88 0x6c 0x45 0xc6 0x3e 0xbf
>>> 0x4c 0x93 0x58 0xe9 0x5c 0x7a 0x63 0xd5
>>> 0x9e 0xb1 0x23 0xf0 0x43 0x50 0x23 0x0d
>>> 0xe8 0xc6 0x9f 0x40 0x79 0x3e 0x5a 0x15
>>> 0xf0 0x4a 0x1a 0x68 0xc5 0xdb 0xb1 0x69
>>> 0x9b 0x5d 0x5c 0x6c 0x12 0x1b 0xaa 0x24
>>> 0x36 0x15 0x11 0x45 0x12 0xe5 0x37 0x85
>>> 0xa4 0xa8 0x59 0xeb 0x2b 0x2c 0xc4 0x14
>>> 0xa4 0x70 0x11 0x72 0x51 0x02 0x03 0x01
>>> 0x00 0x01
>>>
>>> What type encoding is 0x30? I was expecting to see 0x10 (the type value
>> for SEQUENCE).
>> ASN.1 encodes objects as TLV (tag, length, value).
>> Tag is constructed with class, type, object value.
>> If object value is less then 31 all this information is encoded
>> in one byte (class - 2bits, type - 1bit, object value - 5bits).
>> Because ASN.1 SEQUENCE has value of 0x10 (which is less then 31)
>> all this is encoded in one byte as:
>>
>> ASN_CLASS_UNIVERSAL | ASN_TYPE_CONSTRUCTED | ASN_OBJECT_SEQUENCE
>>
>> where:
>> ASN_CLASS_UNIVERSAL = 0x00
>> ASN_TYPE_CONSTRUCTED = 0x20
>> ASN_OBJECT_SEQUENCE = 0x10
>>
>> which gives you 0x30
>>
>> Best regards,
>> --
>> Marek Marcola
>>
>> ______________________________________________________________________
>> OpenSSL Project http://www.openssl.org
>> User Support Mailing List openssl-users@openssl.org
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