Comment 1 by jdnurmi:

Ok, I really wanted this, so I started hacking around to prove I wasn't crazy.
The following will generate a pkcs1 key (only version 0, since I still don't understand
oPI, but that seems to be sufficient to make openssl happy.
*** There's also a flaw in the current implementation I saw -- integers must be encoded
to follow DER, (see http://www.itu.int/ITU-T/studygroups/com17/languages/X.690-0207.pdf
; Section 8.3;);  
This is related to, but not directly fixed by issue/997, as it relates to the encoding
of 'big' to ASN1 (which is done in the PKCS1 Marshalling function of the x509 module).
Since 2s complement encoding is used, so if you have a very large number whose first bit
in the Byte-series is 1, the encoding would be interpreted to be negative by other ASN.1
interpreters.  RSA does not generally use negative numbers.
IMHO, A better solution would be to either always pad the result of big.Byte() if
necessary to represent the sign correctly, or add an big.SignedBytes() internally that
could evaluate the pos/neg of the big;  The below is just a hack to do the encoding
"correctly", so I can generate a PEM.
type otherPrimeInfos struct {
  Prime asn1.RawValue
  Exponent asn1.RawValue
  Coefficient asn1.RawValue
}
type pkcs1Key struct {
  Version int
  N       asn1.RawValue
  E       int
  D       asn1.RawValue
  P       asn1.RawValue
  Q       asn1.RawValue
  Exponent1 asn1.RawValue
  Exponent2 asn1.RawValue
  Coefficient asn1.RawValue
  //OtherPrimeInfos []otherPrimeInfos
}
func BigInt2ASN(t int, b *big.Int)(asn1.RawValue){
  origBytes := b.Bytes()
  if origBytes[0] & 0x80 == 0x80 {
    newBytes := make([]byte, len(origBytes) + 1)
    copy(newBytes[1:], origBytes)
    return asn1.RawValue{Tag: t, Bytes: newBytes}
  }
  return asn1.RawValue{Tag: t, Bytes: origBytes}
}
func setuppkcs1Key(pk *rsa.PrivateKey) (b []byte, err os.Error ){
  k := pkcs1Key {
    Version: 0,
    N: BigInt2ASN(2, pk.N),
    E: pk.PublicKey.E,
    D: BigInt2ASN(2, pk.D),
    P: BigInt2ASN(2, pk.P),
    Q: BigInt2ASN(2, pk.Q),
  }
  //k.OtherPrimeInfos = make([]otherPrimeInfos, 0)
  minusone := big.NewInt(-1)
  one := big.NewInt(1)
  q_1 := big.NewInt(0).Sub(pk.Q, one)
  p_1 := big.NewInt(0).Sub(pk.P, one)
  exp1 := big.NewInt(0).Mod(pk.D, p_1)
  exp2 := big.NewInt(0).Mod(pk.D, q_1)
  coeff := big.NewInt(0).Exp(pk.Q, minusone, pk.P)
  k.Exponent1 = BigInt2ASN(2, exp1)
  k.Exponent2 = BigInt2ASN(2, exp2)
  k.Coefficient = BigInt2ASN(2, coeff)
  b, err = asn1.MarshalToMemory(k)
  return
}

Comment 2:

-> agl for triage

Owner changed to a...@golang.org.

Status changed to Accepted.

Comment 3:

This issue was closed by revision 555685e.

Status changed to Fixed.