[PATCH v2] X.509: unpack RSA signatureValue field from BIT STRING

Maciej S. Szmigiero mail at maciej.szmigiero.name
Tue Apr 17 15:11:54 UTC 2018

On 17.04.2018 17:07, Kamil Konieczny wrote:
> On 17.04.2018 15:39, Maciej S. Szmigiero wrote:
>> The signatureValue field of a X.509 certificate is encoded as a BIT STRING.
>> For RSA signatures this BIT STRING is of so-called primitive subtype, which
>> contains a u8 prefix indicating a count of unused bits in the encoding.
>> We have to strip this prefix from signature data, just as we already do for
>> key data in x509_extract_key_data() function.
>> This wasn't noticed earlier because this prefix byte is zero for RSA key
>> sizes divisible by 8. Since BIT STRING is a big-endian encoding adding zero
>> prefixes has no bearing on its value.
>> The signature length, however was incorrect, which is a problem for RSA
>> implementations that need it to be exactly correct (like AMD CCP).
>> Signed-off-by: Maciej S. Szmigiero <mail at maciej.szmigiero.name>
> your e-mail address looks incorrect
> [...]

What's wrong with it?

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