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/*
* RSA authentication.
*
* Old ssh client protocol:
* read public key
* if you don't like it, read another, repeat
* write challenge
* read response
*
* all numbers are hexadecimal biginits parsable with strtomp.
*
* Sign (PKCS #1 using hash=sha1 or hash=md5)
* write hash(msg)
* read signature(hash(msg))
*
* Verify:
* write hash(msg)
* write signature(hash(msg))
* read ok or fail
*/
#include "dat.h"
enum {
CHavePub,
CHaveResp,
VNeedHash,
VNeedSig,
VHaveResp,
SNeedHash,
SHaveResp,
Maxphase,
};
static char *phasenames[] = {
[CHavePub] "CHavePub",
[CHaveResp] "CHaveResp",
[VNeedHash] "VNeedHash",
[VNeedSig] "VNeedSig",
[VHaveResp] "VHaveResp",
[SNeedHash] "SNeedHash",
[SHaveResp] "SHaveResp",
};
struct State
{
RSApriv *priv;
mpint *resp;
int off;
Key *key;
mpint *digest;
int sigresp;
};
static mpint* mkdigest(RSApub *key, char *hashalg, uchar *hash, uint dlen);
static RSApriv*
readrsapriv(Key *k)
{
char *a;
RSApriv *priv;
priv = rsaprivalloc();
if((a=_strfindattr(k->attr, "ek"))==nil || (priv->pub.ek=strtomp(a, nil, 16, nil))==nil)
goto Error;
if((a=_strfindattr(k->attr, "n"))==nil || (priv->pub.n=strtomp(a, nil, 16, nil))==nil)
goto Error;
if(k->privattr == nil) /* only public half */
return priv;
if((a=_strfindattr(k->privattr, "!p"))==nil || (priv->p=strtomp(a, nil, 16, nil))==nil)
goto Error;
if((a=_strfindattr(k->privattr, "!q"))==nil || (priv->q=strtomp(a, nil, 16, nil))==nil)
goto Error;
if((a=_strfindattr(k->privattr, "!kp"))==nil || (priv->kp=strtomp(a, nil, 16, nil))==nil)
goto Error;
if((a=_strfindattr(k->privattr, "!kq"))==nil || (priv->kq=strtomp(a, nil, 16, nil))==nil)
goto Error;
if((a=_strfindattr(k->privattr, "!c2"))==nil || (priv->c2=strtomp(a, nil, 16, nil))==nil)
goto Error;
if((a=_strfindattr(k->privattr, "!dk"))==nil || (priv->dk=strtomp(a, nil, 16, nil))==nil)
goto Error;
return priv;
Error:
rsaprivfree(priv);
return nil;
}
static int
rsainit(Proto*, Fsstate *fss)
{
Keyinfo ki;
State *s;
char *role;
if((role = _strfindattr(fss->attr, "role")) == nil)
return failure(fss, "rsa role not specified");
if(strcmp(role, "client") == 0)
fss->phase = CHavePub;
else if(strcmp(role, "sign") == 0)
fss->phase = SNeedHash;
else if(strcmp(role, "verify") == 0)
fss->phase = VNeedHash;
else
return failure(fss, "rsa role %s unimplemented", role);
s = emalloc(sizeof *s);
fss->phasename = phasenames;
fss->maxphase = Maxphase;
fss->ps = s;
switch(fss->phase){
case SNeedHash:
case VNeedHash:
mkkeyinfo(&ki, fss, nil);
if(findkey(&s->key, &ki, nil) != RpcOk)
return failure(fss, nil);
/* signing needs private key */
if(fss->phase == SNeedHash && s->key->privattr == nil)
return failure(fss,
"missing private half of key -- cannot sign");
}
return RpcOk;
}
static int
rsaread(Fsstate *fss, void *va, uint *n)
{
RSApriv *priv;
State *s;
mpint *m;
Keyinfo ki;
int len, r;
s = fss->ps;
switch(fss->phase){
default:
return phaseerror(fss, "read");
case CHavePub:
if(s->key){
closekey(s->key);
s->key = nil;
}
mkkeyinfo(&ki, fss, nil);
ki.skip = s->off;
ki.noconf = 1;
if(findkey(&s->key, &ki, nil) != RpcOk)
return failure(fss, nil);
s->off++;
priv = s->key->priv;
*n = snprint(va, *n, "%B", priv->pub.n);
return RpcOk;
case CHaveResp:
*n = snprint(va, *n, "%B", s->resp);
fss->phase = Established;
return RpcOk;
case SHaveResp:
priv = s->key->priv;
len = (mpsignif(priv->pub.n)+7)/8;
if(len > *n)
return failure(fss, "signature buffer too short");
m = rsadecrypt(priv, s->digest, nil);
r = mptobe(m, (uchar*)va, len, nil);
if(r < len){
memmove((uchar*)va+len-r, va, r);
memset(va, 0, len-r);
}
*n = len;
mpfree(m);
fss->phase = Established;
return RpcOk;
case VHaveResp:
*n = snprint(va, *n, "%s", s->sigresp == 0? "ok":
"signature does not verify");
fss->phase = Established;
return RpcOk;
}
}
static int
rsawrite(Fsstate *fss, void *va, uint n)
{
RSApriv *priv;
mpint *m, *mm;
State *s;
char *hash;
int dlen;
s = fss->ps;
switch(fss->phase){
default:
return phaseerror(fss, "write");
case CHavePub:
if(s->key == nil)
return failure(fss, "no current key");
switch(canusekey(fss, s->key)){
case -1:
return RpcConfirm;
case 0:
return failure(fss, "confirmation denied");
case 1:
break;
}
m = strtomp(va, nil, 16, nil);
if(m == nil)
return failure(fss, "invalid challenge value");
m = rsadecrypt(s->key->priv, m, m);
s->resp = m;
fss->phase = CHaveResp;
return RpcOk;
case SNeedHash:
case VNeedHash:
/* get hash type from key */
hash = _strfindattr(s->key->attr, "hash");
if(hash == nil)
hash = "sha1";
if(strcmp(hash, "sha1") == 0)
dlen = SHA1dlen;
else if(strcmp(hash, "md5") == 0)
dlen = MD5dlen;
else
return failure(fss, "unknown hash function %s", hash);
if(n != dlen)
return failure(fss, "hash length %d should be %d",
n, dlen);
priv = s->key->priv;
s->digest = mkdigest(&priv->pub, hash, (uchar *)va, n);
if(s->digest == nil)
return failure(fss, nil);
if(fss->phase == VNeedHash)
fss->phase = VNeedSig;
else
fss->phase = SHaveResp;
return RpcOk;
case VNeedSig:
priv = s->key->priv;
m = betomp((uchar*)va, n, nil);
mm = rsaencrypt(&priv->pub, m, nil);
s->sigresp = mpcmp(s->digest, mm);
mpfree(m);
mpfree(mm);
fss->phase = VHaveResp;
return RpcOk;
}
}
static void
rsaclose(Fsstate *fss)
{
State *s;
s = fss->ps;
if(s->key)
closekey(s->key);
if(s->resp)
mpfree(s->resp);
if(s->digest)
mpfree(s->digest);
free(s);
}
static int
rsaaddkey(Key *k, int before)
{
fmtinstall('B', mpfmt);
if((k->priv = readrsapriv(k)) == nil){
werrstr("malformed key data");
return -1;
}
return replacekey(k, before);
}
static void
rsaclosekey(Key *k)
{
rsaprivfree(k->priv);
}
Proto rsa = {
.name= "rsa",
.init= rsainit,
.write= rsawrite,
.read= rsaread,
.close= rsaclose,
.addkey= rsaaddkey,
.closekey= rsaclosekey,
};
/*
* Simple ASN.1 encodings.
* Lengths < 128 are encoded as 1-bytes constants,
* making our life easy.
*/
/*
* Hash OIDs
*
* SHA1 = 1.3.14.3.2.26
* MDx = 1.2.840.113549.2.x
*/
#define O0(a,b) ((a)*40+(b))
#define O2(x) \
(((x)>> 7)&0x7F)|0x80, \
((x)&0x7F)
#define O3(x) \
(((x)>>14)&0x7F)|0x80, \
(((x)>> 7)&0x7F)|0x80, \
((x)&0x7F)
uchar oidsha1[] = { O0(1, 3), 14, 3, 2, 26 };
uchar oidmd2[] = { O0(1, 2), O2(840), O3(113549), 2, 2 };
uchar oidmd5[] = { O0(1, 2), O2(840), O3(113549), 2, 5 };
/*
* DigestInfo ::= SEQUENCE {
* digestAlgorithm AlgorithmIdentifier,
* digest OCTET STRING
* }
*
* except that OpenSSL seems to sign
*
* DigestInfo ::= SEQUENCE {
* SEQUENCE{ digestAlgorithm AlgorithmIdentifier, NULL }
* digest OCTET STRING
* }
*
* instead. Sigh.
*/
static int
mkasn1(uchar *asn1, char *alg, uchar *d, uint dlen)
{
uchar *obj, *p;
uint olen;
if(strcmp(alg, "sha1") == 0){
obj = oidsha1;
olen = sizeof(oidsha1);
}else if(strcmp(alg, "md5") == 0){
obj = oidmd5;
olen = sizeof(oidmd5);
}else{
sysfatal("bad alg in mkasn1");
return -1;
}
p = asn1;
*p++ = 0x30; /* sequence */
p++;
*p++ = 0x30; /* another sequence */
p++;
*p++ = 0x06; /* object id */
*p++ = olen;
memmove(p, obj, olen);
p += olen;
*p++ = 0x05; /* null */
*p++ = 0;
asn1[3] = p - (asn1+4); /* end of inner sequence */
*p++ = 0x04; /* octet string */
*p++ = dlen;
memmove(p, d, dlen);
p += dlen;
asn1[1] = p - (asn1+2); /* end of outer sequence */
return p - asn1;
}
static mpint*
mkdigest(RSApub *key, char *hashalg, uchar *hash, uint dlen)
{
mpint *m;
uchar asn1[512], *buf;
int len, n, pad;
/*
* Create ASN.1
*/
n = mkasn1(asn1, hashalg, hash, dlen);
/*
* PKCS#1 padding
*/
len = (mpsignif(key->n)+7)/8 - 1;
if(len < n+2){
werrstr("rsa key too short");
return nil;
}
pad = len - (n+2);
buf = emalloc(len);
buf[0] = 0x01;
memset(buf+1, 0xFF, pad);
buf[1+pad] = 0x00;
memmove(buf+1+pad+1, asn1, n);
m = betomp(buf, len, nil);
free(buf);
return m;
}