+
+/*
+ * Save an RSA key file. Return nonzero on success.
+ */
+int saversakey(char *filename, struct RSAKey *key, struct RSAAux *aux,
+ char *passphrase) {
+ unsigned char buf[16384];
+ unsigned char keybuf[16];
+ struct MD5Context md5c;
+ char *p, *estart;
+ FILE *fp;
+
+ /*
+ * Write the initial signature.
+ */
+ p = buf;
+ memcpy(p, rsa_signature, sizeof(rsa_signature));
+ p += sizeof(rsa_signature);
+
+ /*
+ * One byte giving encryption type, and one reserved (zero)
+ * uint32.
+ */
+ *p++ = (passphrase ? SSH_CIPHER_3DES : 0);
+ PUT_32BIT(p, 0); p += 4;
+
+ /*
+ * An ordinary SSH 1 public key consists of: a uint32
+ * containing the bit count, then two bignums containing the
+ * modulus and exponent respectively.
+ */
+ PUT_32BIT(p, ssh1_bignum_bitcount(key->modulus)); p += 4;
+ p += ssh1_write_bignum(p, key->modulus);
+ p += ssh1_write_bignum(p, key->exponent);
+
+ /*
+ * A string containing the comment field.
+ */
+ if (key->comment) {
+ PUT_32BIT(p, strlen(key->comment)); p += 4;
+ memcpy(p, key->comment, strlen(key->comment));
+ p += strlen(key->comment);
+ } else {
+ PUT_32BIT(p, 0); p += 4;
+ }
+
+ /*
+ * The encrypted portion starts here.
+ */
+ estart = p;
+
+ /*
+ * Two bytes, then the same two bytes repeated.
+ */
+ *p++ = random_byte();
+ *p++ = random_byte();
+ p[0] = p[-2]; p[1] = p[-1]; p += 2;
+
+ /*
+ * Four more bignums: the decryption exponent, then iqmp, then
+ * q, then p.
+ */
+ p += ssh1_write_bignum(p, key->private_exponent);
+ p += ssh1_write_bignum(p, aux->iqmp);
+ p += ssh1_write_bignum(p, aux->q);
+ p += ssh1_write_bignum(p, aux->p);
+
+ /*
+ * Now write zeros until the encrypted portion is a multiple of
+ * 8 bytes.
+ */
+ while ((p-estart) % 8)
+ *p++ = '\0';
+
+ /*
+ * Now encrypt the encrypted portion.
+ */
+ if (passphrase) {
+ MD5Init(&md5c);
+ MD5Update(&md5c, passphrase, strlen(passphrase));
+ MD5Final(keybuf, &md5c);
+ des3_encrypt_pubkey(keybuf, estart, p-estart);
+ memset(keybuf, 0, sizeof(keybuf)); /* burn the evidence */
+ }
+
+ /*
+ * Done. Write the result to the file.
+ */
+ fp = fopen(filename, "wb");
+ if (fp) {
+ int ret = (fwrite(buf, 1, p-buf, fp) == (size_t)(p-buf));
+ ret = ret && (fclose(fp) == 0);
+ return ret;
+ } else
+ return 0;
+}