by fabio.pianese:

Probable bug in the crypto/rsa package. GenerateKey is declaring new errs
which override the return value ones. Caller function gets a nil error in
the top scope because the lower scoped error is not bound to the
return. 

What steps will reproduce the problem?
1. generate a rsa private key (let's call it priv)
2. priv.Validate() or any attempt to print fields from priv results in a crash

What is your $GOOS?  $GOARCH?
$ echo $GOOS $GOARCH
linux 386

Which revision are you using?  (hg identify)

$ hg log -l 1
changeset:   4108:d1b75410b793
tag:         tip
user:        Adam Langley <agl@golang.org>
date:        Tue Nov 17 18:21:47 2009 -0800

Please provide any additional information below.

Modifying the GenerateKey function as follows properly returns a EOF error
to the caller. (Thanks to Noah Evans for figuring out the issue!)

----
// GenerateKeyPair generates an RSA keypair of the given bit size.
func GenerateKey(rand io.Reader, bits int) (priv *PrivateKey, err os.Error) {
    priv = new(PrivateKey);
    // Smaller public exponents lead to faster public key
    // operations. Since the exponent must be coprime to
    // (p-1)(q-1), the smallest possible value is 3. Some have
    // suggested that a larger exponent (often 2**16+1) be used
    // since previous implementation bugs[1] were avoided when this
    // was the case. However, there are no current reasons not to use
    // small exponents.
    // [1] http://marc.info/?l=cryptography&;m=115694833312008&w=2
    priv.E = 3;

    pminus1 := new(big.Int);
    qminus1 := new(big.Int);
    totient := new(big.Int);

    for {
        var p, q *big.Int;   // line changed from original
        p, err = randomSafePrime(rand, bits/2);
        if err != nil {
            return
        }

        q, err = randomSafePrime(rand, bits/2);
        if err != nil {
            return
        }

        if p.Cmp(q) == 0 {
            continue
        }

        n := new(big.Int).Mul(p, q);
        pminus1.Sub(p, bigOne);
        qminus1.Sub(q, bigOne);
        totient.Mul(pminus1, qminus1);

        g := new(big.Int);
        priv.D = new(big.Int);
        y := new(big.Int);
        e := big.NewInt(int64(priv.E));
        big.GcdInt(g, priv.D, y, e, totient);

        if g.Cmp(bigOne) == 0 {
            priv.D.Add(priv.D, totient);
            priv.P = p;
            priv.Q = q;
            priv.N = n;

            break;
        }
    }

    return;
}

----