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: [email protected]
> 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
>
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