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Choose better values for internal buffer max size 

2048: 0x3B0 -> 0x3B6 (was actually 6 bytes too small)
3072: 0x570 -> 0x50F (was 61 bytes larger than necessary)
4096: 0x730 -> 0x66D (was 195 bytes larger than necessary)
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c0de 2023-10-04 13:38:28 -05:00
parent 1724975b08
commit 604de144c6
1 changed files with 25 additions and 22 deletions
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README.md
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@ -78,40 +78,43 @@ The repository contains several directories:
- `videos` contains sample videos demonstrating smartcard interactions
with OpenKeychain and K9 mail on Android Nexus 5.
## Build and installation instructions
### Prerequisites
# Build and installation instructions
## Prerequisites
- A Java compiler
- A device compliant with JavaCard 3.0.1 (or above) with enough
available resources to hold the code (approximately 23 kB of
non-volatile memory), persistent data (approximately 10 kB of
non-volatile memory) and volatile data (approximately 2 kB of RAM).
- A Java compiler (No higher than OpenJDK 11 or equivalent)
- A device compliant with JavaCard 3.0.1 (or above) with enough available resources
- Applet: ~23 KiB of non-volatile (eeprom/flash) memory
- Persistant Data: ~10 KiB of non-volatile (eeprom/flash) memory
- Transient Data: ~2 KiB of volatile (RAM) memory
<!-- - The [pyscard](https://pypi.org/project/pyscard/) and [pyasn1](https://pypi.org/project/pyasn1/)
Python libraries for `smartcard-cli`. -->
### Importing RSA keys above 2048 bits
## Importing RSA keys above 2048 bits (3072 or 4096 bits)
The default internal buffer that stores keys is configured with a default
value that is only large enough for RSA 2048 bit keys.
The size of the internal buffer is set by default to a value that
permits to import RSA 2048 bits. If your card is able to deal with RSA
keys of 3072 or 4096 bits and you want to be able to import such keys,
then you need to adjust the size of this buffer:
if your card is able to handle larger RSA key bit-lengths (3072 or 4096),
and you want to import those keys, you will need to increase the buffer size.
- for RSA 2048 bits, `Constants.INTERNAL_BUFFER_MAX_LENGTH` must be at
least `(short)0x3b0`;
This can be accomplished by modifying `Constants.INTERNAL_BUFFER_MAX_LENGTH` in [Constants.java](src/dev/c0de/smartpgp/Constants.java)
- for RSA 3072 bits, `Constants.INTERNAL_BUFFER_MAX_LENGTH` must be at
least `(short)0x570`;
#### RSA 2048 bit keys
- for RSA 4096 bits, `Constants.INTERNAL_BUFFER_MAX_LENGTH` must be at
least `(short)0x730`.
When produced by OpenPGP, these keys are 949 Bytes in length.
`Constants.INTERNAL_BUFFER_MAX_LENGTH` may not be smaller than `(short)0x3b6` (decimal: 950)
#### RSA 3072 bit keys
When produced by OpenPGP, these keys are 1294 Bytes in length.
`Constants.INTERNAL_BUFFER_MAX_LENGTH` may not be smaller than `(short)0x50f` (decimal: 1295)
#### RSA 4096 bit keys
When produced by OpenPGP, these keys are 1644 Bytes in length.
`Constants.INTERNAL_BUFFER_MAX_LENGTH` may not be smaller than `(short)0x66d` (decimal: 1645)
## Reducing flash and/or RAM consumption