I'm a crypto newbie, but have been working on card-access systems that encrypt the card data with 128-bit RSA.

I have an example (from a card) of 1024 bits of encrypted data. I also have the public key (1024 bits), which is (rather curiously) placed into the access-control hardware. I'm 100% sure it's a public (not a private) key.

First attempts with using the key with OpenSSL with the binary key fail:

➤ openssl rsautl -decrypt -in ptt.enc.key -inkey ptt.pub.key -out ptt.dec.hex
unable to load Private Key
➤ 11636:error:0906D06C:PEM routines:PEM_read_bio:no start line:pem_lib.c:648:Expecting: ANY PRIVATE KEY

I'm aware that I need to probably format / prep the key, but I'm not sure how.

Any ideas?

Edit For what it's worth: The public key is:

15 77 D0 29 87 C6 3A 95 B5 1A E1 49 43 08 34 AE AF 3F 2E 0F 4C F8 C6 88 7A C6 C8 D7 32 D7 94 82 60 4F C1 8D A7 7A 9C C1 F5 4D 80 63 EA E6 E4 2A 41 B2 E0 4D 16 63 85 6D 76 0E AB EC CF B7 83 BA E1 D4 3E 1E 02 C5 01 1E 82 3B 24 F2 91 8F 98 A4 96 2A 87 5D 0D F9 4F 80 98 A1 A3 0D C9 41 30 3F 98 AB A1 9E 6F 99 65 97 ED AD 7F 03 CA B9 15 ED 4B 58 B7 BA AD 28 C0 B6 75 93 CD FC CB 53 99 AB

An encrypted card value is:

8F 04 8D E0 83 7F 29 C8 03 54 D1 B5 E3 03 27 4E 3F C5 8D 79 75 D6 A1 FE 3B 67 F1 43 99 65 CC EE B1 A8 55 BA E8 3D A7 81 75 FD 2E 86 B3 A6 C8 A0 4E 0D 77 1E C3 C0 AE 27 DA 06 3D 8F A5 CC E0 32 3D 65 60 E9 86 A2 65 E2 BB D3 B9 37 4E A6 BF 91 89 02 C5 26 E0 AF FD A8 82 23 68 38 4E 26 51 44 52 D9 B6 CA 6E 84 0A 9D 6C FA BE 85 D3 22 DF 57 61 B9 A8 21 0B A4 6D 89 12 4A 64 25 83 12 60 3D

The overall protection works like this: External services can have access to buildings - but each individual access is time limited, to prevent abuse. Cards must be refreshed every day or so.

According to the system documentation:

"Building access is controlled by adding the services' public key to the building's device"

And:

"A service's 'charging device' using RSA encryption using 768 or 1024 bit private keys allows badges to be issued to users on a daily basis"

I agree - this seems to be the inverse of an asynchronous key system (distributing the public key, and then using the private key for encryption) - so perhaps they're doing something different (RSA signing?) - this is what I'm trying to determine.

This is corroborated within the hardware code that I'm seeing:

$PubKey = "x31353737443032393837433633413935423531414531343934333038333441454146334632453046344346384336383837414336433844373332443739343832363034464331384441373741394343314635344438303633454145364534324134314232453034443136363338353644373630454142454343464237383342414531443433453145303243353031314538323342323446323931384639384134393632413837354430444639344638303938413141333044433934313330334639384142413139453646393936353937454441443746303343414239313545443442353842374241414432384330423637353933434446434342353339394142"

Hopefully this edit will provide some clarity on the whole situation - I appreciate your insight and assistance.