(Visual Basic 6.0) Understanding a few ECDSA Public Key Formats

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Describes a few ECDSA public key formats.

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' Here we have the output of the following openssl command:  openssl ec -in key.pem -pubout -text

' Private-Key: (256 bit)
' priv:
'     0e:63:25:8a:73:3c:71:b6:c0:e7:a3:0f:94:b9:74:
'     e0:be:bd:46:18:be:40:7e:66:9e:21:99:85:0e:ed:
'     87:2d
' pub:
'     04:5d:1a:4f:d9:bd:49:9e:e4:fd:55:2c:0d:ea:6d:
'     b1:66:64:7a:71:91:13:63:86:fe:ca:94:d4:47:51:
'     39:66:ff:43:d5:62:de:f2:f2:41:3c:2e:3f:95:18:
'     2d:23:f7:e7:8e:75:19:3b:c6:50:fb:d9:90:f5:e8:
'     12:b7:b8:6a:43
' ASN1 OID: prime256v1
' NIST CURVE: P-256
' writing EC key
' -----BEGIN PUBLIC KEY-----
' MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEXRpP2b1JnuT9VSwN6m2xZmR6cZET
' Y4b+ypTUR1E5Zv9D1WLe8vJBPC4/lRgtI/fnjnUZO8ZQ+9mQ9egSt7hqQw==
' -----END PUBLIC KEY-----

' The public key is shown in two different formats.
' The first is this:

' pub:
'     04:5d:1a:4f:d9:bd:49:9e:e4:fd:55:2c:0d:ea:6d:
'     b1:66:64:7a:71:91:13:63:86:fe:ca:94:d4:47:51:
'     39:66:ff:43:d5:62:de:f2:f2:41:3c:2e:3f:95:18:
'     2d:23:f7:e7:8e:75:19:3b:c6:50:fb:d9:90:f5:e8:
'     12:b7:b8:6a:43

' It is the ANSI X9.63 format.
' 65-bytes are the uncompressed public key (04 || X || Y) 

' This is the same public key, but in PEM format

' -----BEGIN PUBLIC KEY-----
' MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEXRpP2b1JnuT9VSwN6m2xZmR6cZET
' Y4b+ypTUR1E5Zv9D1WLe8vJBPC4/lRgtI/fnjnUZO8ZQ+9mQ9egSt7hqQw==
' -----END PUBLIC KEY-----

' It contains ASN.1 that more explicitly identifies the key type.
' 
' SEQUENCE (2 elem)
'   SEQUENCE (2 elem)
'     OBJECT IDENTIFIER 1.2.840.10045.2.1 ecPublicKey (ANSI X9.62 public key type)
'     OBJECT IDENTIFIER 1.2.840.10045.3.1.7 prime256v1 (ANSI X9.62 named elliptic curve)
'   BIT STRING (520 bit) 000001000101110100011010010011111101100110111101010010011001111011100...

Dim success As Long

' PEM format can be loaded into a Chilkat public key object like this:

Dim sbPem As New ChilkatStringBuilder
success = sbPem.Append("-----BEGIN PUBLIC KEY-----" & vbCrLf)
success = sbPem.Append("MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEXRpP2b1JnuT9VSwN6m2xZmR6cZET" & vbCrLf)
success = sbPem.Append("Y4b+ypTUR1E5Zv9D1WLe8vJBPC4/lRgtI/fnjnUZO8ZQ+9mQ9egSt7hqQw==" & vbCrLf)
success = sbPem.Append("-----END PUBLIC KEY-----" & vbCrLf)

Dim pubKey1 As New PublicKey
success = pubKey1.LoadFromString(sbPem.GetAsString())
If (success = 0) Then
    Debug.Print pubKey1.LastErrorText
    Exit Sub
End If

' The X9.63 format can be loaded like this:
Dim sbHex As New ChilkatStringBuilder
success = sbHex.Append("04:5d:1a:4f:d9:bd:49:9e:e4:fd:55:2c:0d:ea:6d:")
success = sbHex.Append("b1:66:64:7a:71:91:13:63:86:fe:ca:94:d4:47:51:")
success = sbHex.Append("39:66:ff:43:d5:62:de:f2:f2:41:3c:2e:3f:95:18:")
success = sbHex.Append("2d:23:f7:e7:8e:75:19:3b:c6:50:fb:d9:90:f5:e8:")
success = sbHex.Append("12:b7:b8:6a:43")

' Get rid of the ":" chars.
Dim numReplaced As Long
numReplaced = sbHex.Replace(":","")

' We'll need to convert hex to base64..
Dim bdKey As New ChilkatBinData
success = bdKey.AppendEncoded(sbHex.GetAsString(),"hex")

Dim pubKey2 As New PublicKey
success = pubKey2.LoadFromString(bdKey.GetEncoded("base64"))
If (success = 0) Then
    Debug.Print pubKey2.LastErrorText
    Exit Sub
End If

' Let's get the key in pubKey2 as PEM.
' It should be idential to the PEM above.
Debug.Print pubKey2.GetPem(1)

' Here's the output.  You can see it's the same as the PEM above..

' -----BEGIN PUBLIC KEY-----
' MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEXRpP2b1JnuT9VSwN6m2xZmR6cZET
' Y4b+ypTUR1E5Zv9D1WLe8vJBPC4/lRgtI/fnjnUZO8ZQ+9mQ9egSt7hqQw==
' -----END PUBLIC KEY-----