Xbase++

Understanding a few ECDSA Public Key Formats

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Describes a few ECDSA public key formats. Xbase++

LOCAL nSuccess
LOCAL oSbPem
LOCAL oPubKey1
LOCAL oSbHex
LOCAL nNumReplaced
LOCAL oBdKey
LOCAL oPubKey2

nSuccess := 0

//  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...

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

oSbPem := CreateObject("Chilkat.StringBuilder")
oSbPem:Append("-----BEGIN PUBLIC KEY-----" + Chr(13) + Chr(10))
oSbPem:Append("MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEXRpP2b1JnuT9VSwN6m2xZmR6cZET" + Chr(13) + Chr(10))
oSbPem:Append("Y4b+ypTUR1E5Zv9D1WLe8vJBPC4/lRgtI/fnjnUZO8ZQ+9mQ9egSt7hqQw==" + Chr(13) + Chr(10))
oSbPem:Append("-----END PUBLIC KEY-----" + Chr(13) + Chr(10))

oPubKey1 := CreateObject("Chilkat.PublicKey")
nSuccess := oPubKey1:LoadFromString(oSbPem:GetAsString())
IF (nSuccess == 0)
    ? oPubKey1:LastErrorText
    oSbPem:destroy()
    oPubKey1:destroy()
    RETURN
ENDIF

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

//  Get rid of the ":" chars.
nNumReplaced := oSbHex:Replace(":", "")

//  We'll need to convert hex to base64..
oBdKey := CreateObject("Chilkat.BinData")
oBdKey:AppendEncoded(oSbHex:GetAsString(), "hex")

oPubKey2 := CreateObject("Chilkat.PublicKey")
nSuccess := oPubKey2:LoadFromString(oBdKey:GetEncoded("base64"))
IF (nSuccess == 0)
    ? oPubKey2:LastErrorText
    oSbPem:destroy()
    oPubKey1:destroy()
    oSbHex:destroy()
    oBdKey:destroy()
    oPubKey2:destroy()
    RETURN
ENDIF

//  Let's get the key in pubKey2 as PEM.
//  It should be idential to the PEM above.
? oPubKey2: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-----

oSbPem:destroy()
oPubKey1:destroy()
oSbHex:destroy()
oBdKey:destroy()
oPubKey2:destroy()