LIBSEC(2) LIBSEC(2) 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, asn1toRSApriv, decodepem, eggen, egencrypt, egdecrypt, egsign, egverify, egalloc, egfree, egpuballoc, egpubfree, egprivalloc, egprivfree, egsigalloc, egsigfree, egprivtopub - cryptographic security library SYNOPSIS #include <u.h> #include <libc.h> #include <mp.h> #include <libsec.h> void des_key_setup(uchar key[8], ulong schedule[32]) void block_cipher(ulong *schedule, uchar *data, int decrypting) void setupDESstate(DESstate *s, uchar key[8], uchar *ivec) void desCBCencrypt(uchar*, int, DESstate*) void desCBCdecrypt(uchar*, int, DESstate*) void desECBencrypt(uchar*, int, DESstate*) void desECBdecrypt(uchar*, int, DESstate*) void triple_block_cipher(ulong keys[3][32], uchar*, int) void setupDES3state(DES3state *s, uchar key[3][8], uchar *ivec) void des3CBCencrypt(uchar*, int, DES3state*) void des3CBCdecrypt(uchar*, int, DES3state*) void des3ECBencrypt(uchar*, int, DES3state*) void des3ECBdecrypt(uchar*, int, DES3state*) LIBSEC(2) LIBSEC(2) void key_setup(uchar[7], ulong[32]) void des56to64(uchar *k56, uchar *k64) void des64to56(uchar *k64, uchar *k56) DigestState* md4(uchar *data, ulong dlen, uchar *digest, DigestState *state) DigestState* md5(uchar *data, ulong dlen, uchar *digest, DigestState *state) DigestState* sha1(uchar *data, ulong dlen, uchar *digest, DigestState *state) DigestState* hmac_md5(uchar *data, ulong dlen, uchar *key, ulong klen, uchar *digest, DigestState *state) DigestState* hmac_sha1(uchar *data, ulong dlen, uchar *key, ulong klen, uchar *digest, DigestState *state) void setupRC4state(RC4state *s, uchar *seed, int slen) void rc4(RC4state *s, uchar *data, int dlen) void rc4skip(RC4state *s, int nbytes) void rc4back(RC4state *s, int nbytes) RSApriv* rsagen(int nlen, int elen, int nrep) mpint* rsaencrypt(RSApub *k, mpint *in, mpint *out) mpint* rsadecrypt(RSApriv *k, mpint *in, mpint *out) RSApub* rsapuballoc(void) void rsapubfree(RSApub*) RSApriv* rsaprivalloc(void) void rsaprivfree(RSApriv*) RSApub* rsaprivtopub(RSApriv*) RSApub* X509toRSApub(uchar *cert, int ncert, char *name, int nname) RSApriv* asn1toRSApriv(uchar *priv, int npriv) LIBSEC(2) LIBSEC(2) uchar* decodepem(char *s, char *type, uchar *len) EGpriv* eggen(int nlen, int nrep) mpint* egencrypt(EGpub *k, mpint *in, mpint *out) mpint* egdecrypt(EGpriv *k, mpint *in, mpint *out) EGsig* egsign(EGpriv *k, mpint *m) int egverify(EGpub *k, EGsig *sig, mpint *m) EGpub* egpuballoc(void) void egpubfree(EGpub*) EGpriv* egprivalloc(void) void egprivfree(EGpriv*) EGsig* egsigalloc(void) void egsigfree(EGsig*) EGpub* egprivtopub(EGpriv*) int dec64(uchar *out, int lim, char *in, int n) int enc64(char *out, int lim, uchar *in, int n) int dec32(uchar *out, int lim, char *in, int n) int enc32(char *out, int lim, uchar *in, int n) void genrandom(uchar *buf, int nbytes) void prng(uchar *buf, int nbytes) int smallprimetest(mpint *p) int probably_prime(mpint *p, int nrep) void genprime(mpint *p, int n, int nrep) void gensafeprime(mpint *p, mpint *alpha, int n, int accu- racy) void genstrongprime(mpint *p, int n, int nrep) void DSAprimes(mpint *q, mpint *p, uchar seed[SHA1dlen]) DESCRIPTION LIBSEC(2) LIBSEC(2) These routines provide a base for cryptographic security. DES The Digital Encryption Standard (DES) has the most func- tions. 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. The basic DES function, 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 des_key_setup. Since it is a bit awkward, 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 DESstate struc- ture that contains the key schedule and any chained state. SetupDESstate sets up the DESstate structure using the key and an 8 byte initialization vector. Electronic code book, using desECBencrypt and 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. Cipher block chaining mode, using desCBCencrypt and desCBCdecrypt, is more secure. Every block encrypted depends on the initialization vector and all blocks encrypted before it. 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. There are equivalent triple DES functions for each of the DES functions. 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: des56to64 and des64to56 to convert back and forth between the two for- mats. Also a key schedule can be set up from the 7 byte format using key_setup. Secure Hashes We support several secure hash functions. The output of the hash is called a digest. A hash is secure if, given the LIBSEC(2) LIBSEC(2) 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. The routines md4, md5, sha1, hmac_md5, and hmac_sha1 differ only in the length of the resulting digest and in the secu- rity of the hash. Usage for each is the same. The first call to the routine should have nil as the state parameter. This call returns a state which can be used to chain subse- quent calls. The last call should have digest non-nil. 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 digest. For example, to hash a single buffer using md5: uchar digest[MD5dlen]; md5(data, len, digest, nil); To chain a number of buffers together, bounded on each end by some secret: char buf[256]; uchar digest[MD5dlen]; DigestState *s; 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); The constants MD4dlen, MD5dlen, and SHA1dlen define the lengths of the digests. Hmac_md5 and 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 MD5dlen and SHA1dlen respectively. Alleged RC4 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 setupRC4state, can be any length. The generator can be run forward using rc4, skip over bytes using rc4skip to account lost transmissions, or run back- wards using rc4back to cover retransmitted data. The RC4state structure keeps track of the algorithm. LIBSEC(2) LIBSEC(2) RSA RSA is a public key encryption algorithm. The owner of a key publishes the public part of the key: struct RSApub { mpint *n; // modulus mpint *ek; // exp (encryption key) }; This part can be used for encrypting data (with rsaencrypt) to be sent to the owner. The owner decrypts (with rsadecrypt) using his private key: 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 }; Keys are generated using rsagen. 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. Rsagen returns a newly allocated structure containing both public and private keys. Rsaprivtopub returns a newly allocated copy of the public key corresponding to the private key. The routines rsaalloc, rsafree, rsapuballoc, rsapubfree, rsaprivalloc, and rsaprivfree are provided to aid in user provided key I/O. Given a binary X.509 cert, the routine X509toRSApub returns the public key and, if 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 verifica- tion is done of the certificate signature; the caller should check the fingerprint, sha1(cert), against a table or check the certificate by other means. X.509 certificates are often stored in PEM format; use dec64 to convert to binary before computing the fingerprint or calling X509toRSApub. Asn1toRSApriv converts an ASN1 formatted RSA private key into the corresponding RSApriv structure. Decodepem takes a zero terminated string, s, and decodes the LIBSEC(2) LIBSEC(2) PEM (privacy-enhanced mail) formatted section for type within it. If successful, it returns the decoded section and sets *len to its decoded length. If not, it returns nil, and *len is undefined. ElGamal The corresponding keys for the ElGamal algorithm are: struct EGpub { mpint *p; // modulus mpint *alpha; // generator mpint *key; // (encryption key) alpha**secret mod p }; and struct EGpriv { EGpub pub; mpint *secret; // (decryption key) }; Egsign signs message m using a private key k yielding a struct EGsig { mpint *r, *s; }; Egverify returns 0 if the signature is valid and -1 if not. Encodings 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 char- acter set. Base 64 can encode buffers of any length while base 32 only works on buffers a multiple of 5 bytes long. Enc32 and 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 lim, the length of the output buffer, is too small. Also, for base 32, the encoding fails if the input buffer length, n, is not a multiple of 5. Dec32 and 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. Random numbers Most security software requires a source of random or, at the very least, unguessable numbers. Genrandom fills a buffer with bytes from the X9.17 pseudo- LIBSEC(2) LIBSEC(2) random number generator. The X9.17 generator is seeded by 24 truly random bytes read from /dev/random. Prng uses the native rand(2) pseudo-random number generator to fill the buffer. Used with srand, this function can pro- duce a reproducible stream of pseudo random numbers useful in testing. Both functions may be passed to mprand (see mp(2)). Prime numbers Public key algorithms abound in prime numbers. The follow- ing routines generate primes or test numbers for primality. Smallprimetest checks for divisibility by the first 10000 primes. It returns 0 if p is not divisible by the primes and -1 if it is. Probably_prime uses the Miller-Rabin test to test p. It returns non-zero if P is probably prime. The probability of it not being prime is 1/4**nrep. Genprime generates a random n bit prime. Since it uses the Miller-Rabin test, nrep is the repetition count passed to probably_prime. Gensafegprime generates an n-bit prime p and a generator alpha of the multiplicative group of integers mod p; there is a prime q such that p-1=2*q. Genstrongprime generates a prime, p, with the following properties: - p-1 has a large prime factor, p'. A large factor is one close to 1/2 the bit length of p. - p'-1 has a large prime factor - p+1 has a large prime factor - (p-1)/2 is prime DSAprimes generates two primes, q and p, using the NIST rec- ommended algorithm for DSA primes. q divides p-1. SOURCE /sys/src/libsec SEE ALSO mp(2)