TH LIBSEC 2
SH NAME
setupDESstate, des_key_setup, block_cipher, desCBCencrypt, desCBCdecrypt, desECBencrypt, desECBdecrypt, des3CBCencrypt, des3CBCdecrypt, des3ECBencrypt, des3ECBdecrypt, key_setup, des56to64, des64to56, setupDES3state, triple_block_cipher, md4, md5, sha1, hmac_md5, hmac_sha1, dec64, enc64, dec32, enc32, genrandom, prng, genprime, gensafeprime, genstrongprime, DSAprimes, probably_prime, smallprimetest, setupRC4state, rc4, rc4skip, rc4back, crtpre, crtin, crtout, crtprefree, crtresfree, rsagen, rsaencrypt, rsadecrypt, rsaalloc, rsafree, rsapuballoc, rsapubfree, rsaprivalloc, rsaprivfree, rsaprivtopub, X509toRSApub, eggen, egencrypt, egdecrypt, egsign, egverify, egalloc, egfree, egpuballoc, egpubfree, egprivalloc, egprivfree, egsigalloc, egsigfree, egprivtopub \- cryptographic security library
SH SYNOPSIS
B #include <u.h>
br
B #include <libc.h>
br
B #include <mp.h>
br
B #include <libsec.h>
PP
B
void des_key_setup(uchar key[8], ulong schedule[32])
PP
B
void block_cipher(ulong *schedule, uchar *data,
B
int decrypting)
PP
B
void setupDESstate(DESstate *s, uchar key[8], uchar *ivec)
PP
B
void desCBCencrypt(uchar*, int, DESstate*)
PP
B
void desCBCdecrypt(uchar*, int, DESstate*)
PP
B
void desECBencrypt(uchar*, int, DESstate*)
PP
B
void desECBdecrypt(uchar*, int, DESstate*)
PP
B
void triple_block_cipher(ulong keys[3][32], uchar*, int)
PP
B
void setupDES3state(DES3state *s, uchar key[3][8],
B
uchar *ivec)
PP
B
void des3CBCencrypt(uchar*, int, DES3state*)
PP
B
void des3CBCdecrypt(uchar*, int, DES3state*)
PP
B
void des3ECBencrypt(uchar*, int, DES3state*)
PP
B
void des3ECBdecrypt(uchar*, int, DES3state*)
PP
B
void key_setup(uchar[7], ulong[32])
PP
B
void des56to64(uchar *k56, uchar *k64)
PP
B
void des64to56(uchar *k64, uchar *k56)
PP
B
DigestState* md4(uchar *data, ulong dlen, uchar *digest,
B
DigestState *state)
PP
B
DigestState* md5(uchar *data, ulong dlen, uchar *digest,
B
DigestState *state)
PP
B
DigestState* sha1(uchar *data, ulong dlen, uchar *digest,
B
DigestState *state)
PP
B
DigestState* hmac_md5(uchar *data, ulong dlen,
br
B
uchar *key, ulong klen,
br
B
uchar *digest, DigestState *state)
PP
B
DigestState* hmac_sha1(uchar *data, ulong dlen,
br
B
uchar *key, ulong klen,
br
B
uchar *digest, DigestState *state)
PP
B
void setupRC4state(RC4state *s, uchar *seed, int slen)
PP
B
void rc4(RC4state *s, uchar *data, int dlen)
PP
B
void rc4skip(RC4state *s, int nbytes)
PP
B
void rc4back(RC4state *s, int nbytes)
PP
B
RSApriv* rsagen(int nlen, int elen, int nrep)
PP
B
mpint* rsaencrypt(RSApub *k, mpint *in, mpint *out)
PP
B
mpint* rsadecrypt(RSApriv *k, mpint *in, mpint *out)
PP
B
RSApub* rsapuballoc(void)
PP
B
void rsapubfree(RSApub*)
PP
B
RSApriv* rsaprivalloc(void)
PP
B
void rsaprivfree(RSApriv*)
PP
B
RSApub* rsaprivtopub(RSApriv*)
PP
B
RSApub* X509toRSApub(uchar *cert, int ncert, char *name, int nname)
PP
B
EGpriv* eggen(int nlen, int nrep)
PP
B
mpint* egencrypt(EGpub *k, mpint *in, mpint *out)
PP
B
mpint* egdecrypt(EGpriv *k, mpint *in, mpint *out)
PP
B
EGsig* egsign(EGpriv *k, mpint *m)
PP
B
int egverify(EGpub *k, EGsig *sig, mpint *m)
PP
B
EGpub* egpuballoc(void)
PP
B
void egpubfree(EGpub*)
PP
B
EGpriv* egprivalloc(void)
PP
B
void egprivfree(EGpriv*)
PP
B
EGsig* egsigalloc(void)
PP
B
void egsigfree(EGsig*)
PP
B
EGpub* egprivtopub(EGpriv*)
PP
B
int dec64(uchar *out, int lim, char *in, int n)
PP
B
int enc64(char *out, int lim, uchar *in, int n)
PP
B
int dec32(uchar *out, int lim, char *in, int n)
PP
B
int enc32(char *out, int lim, uchar *in, int n)
PP
B
void genrandom(uchar *buf, int nbytes)
PP
B
void prng(uchar *buf, int nbytes)
PP
B
int smallprimetest(mpint *p)
PP
B
int probably_prime(mpint *p, int nrep)
PP
B
void genprime(mpint *p, int n, int nrep)
PP
B
void gensafeprime(mpint *p, mpint *alpha, int n, int accuracy)
PP
B
void genstrongprime(mpint *p, int n, int nrep)
PP
B
void DSAprimes(mpint *q, mpint *p, uchar seed[SHA1dlen])
SH DESCRIPTION
PP
These routines provide a base for cryptographic security.
SS DES
PP
The Digital Encryption Standard (DES) has the most functions.
It is a shared key or symmetric encryption using either
a 56 bit key for single DES or three 56 bit keys for triple des.
The keys are encoded into 64 bits where every eight bit
is parity.
PP
The basic DES function,
IR block_cipher ,
works on a block of 8 bytes, converting them in place.
It takes a key schedule, a pointer to the block, and
a flag indicating encrypting (0) or decrypting (1).
The key schedule is created from the key using
IR des_key_setup .
PP
Since it is a bit awkward,
I block_cipher
is rarely called directly. Instead, one normally uses
routines that encrypt larger buffers of data and
which may chain the encryption state from one buffer
to the next.
These routines keep track of the state of the
encryption using a
B DESstate
structure that contains the key schedule and any chained
state.
I SetupDESstate
sets up the
B DESstate
structure using the key and an 8 byte initialization vector.
PP
Electronic code book, using
I desECBencrypt
and
IR desECBdecrypt ,
is the less secure mode. The encryption of each 8 bytes
does not depend on the encryption of any other.
Hence the encryption is a substitution
cipher using 64 bit characters.
PP
Cipher block chaining mode, using
I desCBCencrypt
and
IR desCBCdecrypt ,
is more secure. Every block encrypted depends on the initialization
vector and all blocks encrypted before it.
PP
For both CBC and ECB modes, a stream of data can be encrypted as
multiple buffers. However, all buffers except the last must
be a multiple of 8 bytes to ensure successful decryption of
the stream.
PP
There are equivalent triple DES functions for each of the
DES functions.
PP
In the past Plan 9 used a 56 bit or 7 byte
format for DES keys. To be compatible with the rest
of the world, we've abandoned this format.
There are two functions:
I des56to64
and
I des64to56
to convert back and forth between the two formats.
Also a key schedule can be set up from the 7 byte format
using
IR key_setup .
SS "Secure Hashes
PP
We support several secure hash functions. The output of the
hash is called a
IR digest .
A hash is secure if, given the hashed data and the digest,
it is difficult to predict the change to the digest resulting
from some change to the data without rehashing
the whole data. Therefore, if a secret is part of the hashed
data, the digest can be used as an integrity check of the data by anyone
possessing the secret.
PP
The routines
IR md4 ,
IR md5 ,
IR sha1 ,
IR hmac_md5 ,
and
I hmac_sha1
differ only in the length of the resulting digest
and in the security of the hash. Usage for each is the same.
The first call to the routine should have
B nil
as the
I state
parameter. This call returns a state which can be used to chain
subsequent calls.
The last call should have digest non-\fBnil\fR.
I Digest
must point to a buffer of at least the size of the digest produced.
This last call will free the state and copy the result into
IR digest .
For example, to hash a single buffer using
IR md5 :
EX
uchar digest[MD5dlen];
md5(data, len, digest, nil);
EE
PP
To chain a number of buffers together,
bounded on each end by some secret:
EX
s = md5("my password", 11, nil, nil);
while((n = read(fd, buf, 256)) > 0)
md5(buf, n, nil, s);
md5("drowssap ym", 11, digest, s);
EE
PP
The constants
IR MD4dlen ,
IR MD5dlen ,
and
I SHA1dlen
define the lengths of the digests.
PP
I Hmac_md5
and
I hmac_sha1
are used slightly differently. These hash algorithms are keyed and require
a key to be specified on every call.
The digest lengths for these hashes are
I MD5dlen
and
I SHA1dlen
respectively.
SS "Alleged RC4
PP
This is an algorithm alleged to be Rivest's RC4 encryption function. It is
a pseudo-random number generator with a 256 byte state and a long
cycle. The input buffer is XOR'd with the output of the
generator both to encrypt and to decrypt. The seed, entered
using
IR setupRC4state ,
can be any length. The generator can be run forward using
IR rc4 ,
skip over bytes using
I rc4skip
to account lost transmissions,
or run backwards using
I rc4back
to cover retransmitted data.
The
I RC4state
structure keeps track of the algorithm.
SS RSA
PP
RSA is a public key encryption algorithm. The owner of a key publishes
the public part of the key:
EX
struct RSApub
{
mpint *n; // modulus
mpint *ek; // exp (encryption key)
};
EE
This part can be used for encrypting data (with
IR rsaencrypt )
to be sent to the owner.
The owner decrypts (with
IR rsadecrypt )
using his private key:
EX
struct RSApriv
{
RSApub pub;
mpint *dk; // exp (decryption key)
// precomputed crt values
mpint *p;
mpint *q;
mpint *kp; // k mod p-1
mpint *kq; // k mod q-1
mpint *c2; // for converting residues to number
};
EE
PP
Keys are generated using
IR rsagen .
I Rsagen
takes both bit length of the modulus, the bit length of the
public key exponent, and the number of repetitions of the miller-rabin
primality test to run. If the latter is 0, it does the default number
of rounds.
I Rsagen
returns a newly allocated structure containing both
public and private keys.
I Rsaprivtopub
returns a newly allocated copy of the public key
corresponding to the private key.
PP
The routines
IR rsaalloc ,
IR rsafree ,
IR rsapuballoc ,
IR rsapubfree ,
IR rsaprivalloc ,
and
I rsaprivfree
are provided to aid in user provided key I/O.
PP
Given a binary X.509
IR cert ,
the routine
I X509toRSApub
returns the public key and, if
I name
is not nil, the CN part of the Distinguished Name of the
certificate's Subject.
(This is conventionally a userid or a host DNS name.)
No verification is done of the certificate signature; the
caller should check the fingerprint,
IR sha1(cert) ,
against a table or check the certificate by other means.
X.509 certificates are often stored in PEM format; use
I dec64
to convert to binary before computing the fingerprint or calling
IR X509toRSApub .
SS ElGamal
PP
The corresponding keys for the ElGamal algorithm are:
EX
struct EGpub
{
mpint *p; // modulus
mpint *alpha; // generator
mpint *key; // (encryption key) alpha**secret mod p
};
EE
and
EX
struct EGpriv
{
EGpub pub;
mpint *secret; // (decryption key)
};
EE
I Egsign
signs message
I m
using a private key
I k
yielding a
EX
struct EGsig
{
mpint *r, *s;
};
EE
I Egverify
returns 0 if the signature is valid and \-1 if not.
SS Encodings
PP
Two readable and 7-bit safe encodings exist for binary data; base 64 and base 32.
Base 64 is the more compact and more popular, used by MIME and HTTP.
Base 32 is preferred when human transmission is involved. It avoids confusion
by not including upper case or '0', 'o', '1', and 'l' in its character
set. Base 64 can encode buffers of any length while base 32 only
works on buffers a multiple of 5 bytes long.
PP
I Enc32
and
I enc64
both create null terminated strings. They return the size of the
encoded string (without the null) or -1 if the encoding fails.
The encoding fails if
IR lim ,
the length of the output buffer, is too small. Also, for base 32,
the encoding fails if the input buffer length,
IR n ,
is not a multiple of 5.
PP
I Dec32
and
I dec64
return the number of bytes decoded or -1 if the decoding fails.
The decoding fails if the output buffer is not large enough or,
for base 32, if the input buffer length is not a multiple
of 8.
SS "Random numbers
PP
Most security software requires a source of random or, at the
very least, unguessable numbers.
PP
I Genrandom
fills a buffer with bytes from the X9.17 pseudo-random
number generator. The X9.17 generator is seeded by 24
truly random bytes read from
BR /dev/random .
PP
I Prng
uses the native
IR rand (2)
pseudo-random number generator to fill the buffer. Used with
IR srand ,
this function can produce a reproducible stream of pseudo random
numbers useful in testing.
PP
Both functions may be passed to
I mprand
(see
IR mp (2)).
SS "Prime numbers
PP
Public key algorithms abound in prime numbers. The following routines
generate primes or test numbers for primality.
PP
I Smallprimetest
checks for divisibility by the first 10000 primes. It returns 0
if
I p
is not divisible by the primes and \-1 if it is.
PP
I Probably_prime
uses the Miller-Rabin test to test
IR p .
It returns non-zero if
I P
is probably prime. The probability of it not being prime is
1/4**\fInrep\fR.
PP
I Genprime
generates a random
I n
bit prime. Since it uses the Miller-Rabin test,
I nrep
is the repetition count passed to
IR probably_prime .
I Gensafegprime
generates an
IR n -bit
prime
I p
and a generator
I alpha
of the multiplicative group of integers mod \fIp\fR;
there is a prime \fIq\fR such that \fIp-1=2*q\fR.
I Genstrongprime
generates a prime,
IR p ,
with the following properties:
IP \-
IR p -1
has a large prime factor,
IR p '.
A large factor is one close to 1/2
the bit length of
IR p .
IP \-
IR p '-1
has a large prime factor
IP \-
IR p +1
has a large prime factor
IP \-
(\fIp\fR-1)/2 is prime
PP
I DSAprimes
generates two primes,
I q
and
IR p,
using the NIST recommended algorithm for DSA primes.
I q
divides
IR p -1.
SH SOURCE
B /sys/src/libsec
SH SEE ALSO
IR mp (2)
