I draw to your attention that it really is 64 characters, not 64 bytes.  If you 
use utf8String, bmpString, or universalString it can be much longer than 64 
bytes when encoded in DER.  (X.690, 51.5.4, “The count of the number of 
characters … shall be clearly distinguished from a count of octets.”)  So I’m 
not sure what the IDN problem is.  The standard does allow for abbreviations.  
This also seems to me like something that should be argued in the PKIX working 
group or the ITU, not the CABforum.  (The original spec for this value is ITU 
X.411, I think, but not for all the limits, which explains why the limits are 
inconsistently 64 or 128.)

[JR] I realize this is characters but there are definitely names longer than 64 
characters out there. I guess the easy way is to get a DBA in all cases where 
the name is too long.

It is not clear to me in what way 2047 == 2048 and why the same logic can’t be 
applied repeatedly to say that 1024 == 2048.

[JR] See Peter Bowen's email for the explanation:
" I think there is a misunderstanding here. There has never been a requirement 
that the modulus contain a certain number of bits set to ‘1’.  What is required 
is that the modulus be a 2048-bit number.  The problem is that a 2048-bit 
number can have one or more of the high order bits being zero.  When 
calculating the modulus “size”, all an observer can do find the left-most bit 
set to ‘1’ and use that.  RSA moduli normally are the product of two prime 
numbers. OpenSSL and some other generating tools have a function that makes the 
top bit of each prime number to be 1 which ensures the result will have the top 
bit set to 1.  However a random prime could be smaller, resulting in a smaller 
results."

TeletexString is an abomination, and deprecated by the ITU, and not allowed by 
PKIX except for backwards compatibility, and it is not implemented completely 
in any implementation that I know of.
[JR] That's fine. This was more a point of curiosity.

For serial numbers, is there actually a jurisdiction that does this?  It seems 
unlikely, most of the places which might want to do it need serial numbers to 
identify companies with something which can be represented in ASCII.

[JR] Let me see what I can dig out. I was wondering why this is required to be 
printable string instead of UTF8. Any insight on that?

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