ft_rsa

Simple crypto library. RSA, ASN.1, PEM, DER, DES, Base64, SHAx, MD5

About

The goals of this project:

• Pseudo-random number generator
• Password based key derivation
• RSA key generation
• RSA crypt
• RSA utilities
• DES crypt
• Message digest
• Base64 encoding
• ASN.1 tree
• DER encoding
• PEM encoding
• OpenSSL style flags

This project also includes:

• bnum library (big number implementation)
• libft library (partial implementation of libc functions)

Requirements

• GNU C
• MacOS High Sierra or higher
• Ubuntu 16.04 or higher

Limitations

bnum library supports big ints up to 8192 bits. This is because big int's values are stored in stack memory. Since bnum library is used mainly for RSA operations and RSA keysize is usually less than 8192 bits, this limitation should not be important in practice.

During DES crypt operations on a file, whole file is read into memory, which implies system memory limitations for large files.

Although standard recommends that number of trials in Miller-Rabin prime check should change depending on number size, this implemetation uses fixed number of trials, specifically 20 (defined by RM_TRIALS). This results in lower performance when prime checks are performed on 4096 bit or larger numbers.

Compile

make

Usage

Usage is quite similar to openssl, although some flags are different

Digest commands: md5, sha1, sha224, sha256, sha384, sha512, sha512/224, sha512/256

    <file>              read message from <file>
    -p                  read message from stdin
    -r                  reverse output format
    -q                  quiet mode
    -s <string>         input <string>

DES cipher commands: des-ecb, des-cbc

    -a                  base64-encode output / base64-decode input (depending on DES mode)
    -i <file>           read message from <file>
    -o <file>           write output to <file>
    -e                  DES encryption mode (default)
    -d                  DES decryption mode
    -k <key>            hex key input
    -s <salt>           hex salt input
    -p <pass>           password input

Base64 commands: base64

    -i <file>           read message from <file>
    -o <file>           write output to <file>
    -e                  base64 encode mode (default)
    -d                  base64 decode mode
    -b <num>            set output line width to <num>

RSA commands:

    genrsa (generate RSA private keys):
    
    -rand <files>       set rand source as list of <files>, separated by colon
    -o <keyfile>        output generated key to a <keyfile>
    <keysize>           set RSA key size to <keysize> (shall be last argument)
    
    rsa (perform operation on RSA keys):
    
    -in <keyfile>       read input key from <keyfile>
    -out <keyfile>      output key to <keyfile>
    -inform <PEM|DER>   set format of the input key, default is PEM-encoded
    -outform <PEM|DER>  set format of the output key, default is PEM-encoded
    -pubin              input key is a X.509 public key
    -pubout             output key as X.509 public key
    -check              check RSA private key
    -passin:<pass>      set <pass> as password for input key
    -passout:<pass>     set <pass> as password for output key
    -des                encrypt output key using DES-CBC (key outform shall be PEM)
    -text               print input key components
    -noout              do not output key
    -modulus            print input key modulus
    
    rsautl (perform RSA crypt):
    
    -in <file>          read message/cipher form <file>
    -out <file>         write output to a <file>
    -inkey <keyfile>    read RSA key form <keyfile>
    -encrypt            RSA encryption mode (default)
    -decrypt            RSA decryption mode
    -pubin              input key is a X.509 public key
    -hexdump            hexdump output

Usage examples

Generate RSA private key:

./ft_ssl genrsa -o <key> 2048

Check RSA key and print its components:

./ft_ssl rsa -in <key> -check -text -noout

Encrypt message using RSA algorithm:

./ft_ssl rsautl -in <message> -out <cipher> -inkey <key>

References

• LibTomMath, Multi-Precision Math: Tom St Denis, Mads Rasmussen, Greg Rose
• ITU-T X.660: General procedures and top arcs of the international object identifier tree
• ITU-T X.690: Abstract Syntax Notation One (ASN.1)
• FIPS 180-4: Secure Hash Standard
• FIPS 186-4: Digital Signature Standard
• RFC 5280: Internet X.509 Public Key Infrastructure Certificate
• RFC 3447: PKCS #1: RSA Cryptography Specifications Version 2.1
• RFC 8017: PKCS #1: RSA Cryptography Specifications Version 2.2
• RFC 5208: PKCS #8: Private-Key Information Syntax Specification Version 1.2
• RFC 5958: Asymmetric Key Packages
• RFC 7468: Textual Encodings of PKIX, PKCS, and CMS Structures
• RFC 6234: US Secure Hash Algorithms (SHA and SHA-based HMAC and HKDF)
• RFC 1321: The MD5 Message-Digest Algorithm
• FIPS 46-3: Data Encryption Standard (DES)
• RFC 1829: The ESP DES-CBC Transform