Can I build an RSA private key from an OpenSSL configuration file?

Yes, you can build an RSA private key from an OpenSSL configuration file, if you know the components of the key, as shown in the test below:

C:\Users\fyicenter>type asn1_rsa_pri_key.cnf
asn1 = SEQUENCE:rsa_pri_key

[rsa_pri_key]
version=INTEGER:0
n      =INTEGER:0xBB6FE79432CC6EA2D8F970675A5A87BFBE1AFF0BE63E879F2AFFB9\
3644D4D2C6D000430DEC66ABF47829E74B8C5108623A1C0EE8BE217B3AD8D36D5EB4FCA1D9
e      =INTEGER:0x010001
d      =INTEGER:0x6F05EAD2F27FFAEC84BEC360C4B928FD5F3A9865D0FCAAD291E2A5\
2F4AF810DC6373278C006A0ABBA27DC8C63BF97F7E666E27C5284D7D3B1FFFE16B7A87B51D
p      =INTEGER:0xF3929B9435608F8A22C208D86795271D54EBDFB09DDEF539AB083D\
A912D4BD57
q      =INTEGER:0xC50016F89DFF2561347ED1186A46E150E28BF2D0F539A1594BBD7F\
E46746EC4F
exp1   =INTEGER:0x9E7D4326C924AFC1DEA40B45650134966D6F9DFA3A7F9D698CD4AB\
EA9C0A39B9
exp2   =INTEGER:0xBA84003BB95355AFB7C50DF140C60513D0BA51D637272E355E3977\
79E7B2458F
coeff  =INTEGER:0x30B9E4F2AFA5AC679F920FC83F1F2DF1BAF1779CF989447FABC2F5\
628657053A

C:\Users\fyicenter>\local\openssl\openssl asn1parse -genc
onf asn1_rsa_pri_key.cnf -noout -out rsa_pri_key.der

C:\Users\fyicenter>\local\openssl\openssl 
   pkey -in rsa_pri_key.der -inform DER -text -noout
Private-Key: (512 bit)
modulus:
    00:bb:6f:e7:94:32:cc:6e:a2:d8:f9:70:67:5a:5a:
    87:bf:be:1a:ff:0b:e6:3e:87:9f:2a:ff:b9:36:44:
    d4:d2:c6:d0:00:43:0d:ec:66:ab:f4:78:29:e7:4b:
    8c:51:08:62:3a:1c:0e:e8:be:21:7b:3a:d8:d3:6d:
    5e:b4:fc:a1:d9
publicExponent: 65537 (0x10001)
privateExponent:
    6f:05:ea:d2:f2:7f:fa:ec:84:be:c3:60:c4:b9:28:
    fd:5f:3a:98:65:d0:fc:aa:d2:91:e2:a5:2f:4a:f8:
    10:dc:63:73:27:8c:00:6a:0a:bb:a2:7d:c8:c6:3b:
    f9:7f:7e:66:6e:27:c5:28:4d:7d:3b:1f:ff:e1:6b:
    7a:87:b5:1d
prime1:
    00:f3:92:9b:94:35:60:8f:8a:22:c2:08:d8:67:95:
    27:1d:54:eb:df:b0:9d:de:f5:39:ab:08:3d:a9:12:
    d4:bd:57
prime2:
    00:c5:00:16:f8:9d:ff:25:61:34:7e:d1:18:6a:46:
    e1:50:e2:8b:f2:d0:f5:39:a1:59:4b:bd:7f:e4:67:
    46:ec:4f
exponent1:
    00:9e:7d:43:26:c9:24:af:c1:de:a4:0b:45:65:01:
    34:96:6d:6f:9d:fa:3a:7f:9d:69:8c:d4:ab:ea:9c:
    0a:39:b9
exponent2:
    00:ba:84:00:3b:b9:53:55:af:b7:c5:0d:f1:40:c6:
    05:13:d0:ba:51:d6:37:27:2e:35:5e:39:77:79:e7:
    b2:45:8f
coefficient:
    30:b9:e4:f2:af:a5:ac:67:9f:92:0f:c8:3f:1f:2d:
    f1:ba:f1:77:9c:f9:89:44:7f:ab:c2:f5:62:86:57:
    05:3a

⇒ OpenSSL "ans1parse" - RSA Public Key in ASN.1 Structure

⇐ OpenSSL "ans1parse" - RSA Private Key in ASN.1 Structure

⇑ OpenSSL "ans1parse" Command

⇑⇑ OpenSSL Tutorials