How to determine the number of bits used when generating a CSR

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I was looking for an answer to this question today and stumbled across a page on the MaximumASP site, which indicates that looking at the first few characters of the CSR will provide the answer.

I still want to do a bit of research to verify that what they have said is true, but it seems to be, based on my limited test. I generated CSRs for 512-, 1024-, 2048-, 4096-, 8192-, and 16384-bits* and examined the first few characters. My generated CSRs for 512- and 1024-bits matched the MaximumASP page. Here are my results.

512-bit CSR (for 40-Bit certificate)

—–BEGIN NEW CERTIFICATE REQUEST—–
MIIC…

1024-bit CSR (for 128-Bit certificate)

—–BEGIN NEW CERTIFICATE REQUEST—–
MIID…

2048-bit CSR

—–BEGIN NEW CERTIFICATE REQUEST—–
MIIE…

4096-bit CSR

—–BEGIN NEW CERTIFICATE REQUEST—–
MIIG…

8192-bit CSR

—–BEGIN NEW CERTIFICATE REQUEST—–
MIIK…

16384-bit CSR

—–BEGIN NEW CERTIFICATE REQUEST—–
MIIS…

* I knew it was going to take a while generated the 16384-bit CSR, but I didn’t realize it was going to take 7.5 hours! The 8192-bit CSR, in comparison, only took about 20 minutes to generate.

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